pre_text: Interest expense and financing costs Fees and discounts associated with the issuance of our debt instruments are recorded as debt discount, which reduces their respective carrying values, and are amortized over their respective terms. Amortization expense is recorded within “Interest and other expense (income), net” in our consolidated statement of operations. For the years ended December 31, 2019, 2018, and 2017: interest expense was $86 million, $134 million, and $150 million, respectively; amortization of the debt discount and deferred financing costs was $4 million, $6 million, and $12 million, respectively. A summary of our outstanding debt is as follows (amounts in millions): With the exception of the 2026 and the 2047 Notes, using Level 2 inputs (i.e., observable market prices in less-than-active markets) at December 31, 2019, the carrying values of the Notes approximated their fair values, as the interest rates were similar to the current rates at which we could borrow funds over the selected interest periods. At December 31, 2019, based on Level 2 inputs, the fair value of the 2026 and the 2047 Notes were $893 million and $456 million, respectively. Using Level 2 inputs at December 31, 2018, the carrying values of the 2021 Notes and the 2022 Notes approximated their fair values, as the interest rates were similar to the current rates at which we could borrow funds over the selected interest periods. At December 31, 2019, based on Level 2 inputs, the fair values of the 2026 Notes, the 2027 Notes, and the 2047 Notes were $800 million, $376 million, and $360 million, respectively.
table: At December 31, 2019
table: Gross Carrying Amount Unamortized Discount and Deferred Financing Costs Net Carrying Amount
table: 2021 Notes $650 $(2) $648
table: 2022 Notes 400 (2) 398
table: 2026 Notes 850 (7) 843
table: 2027 Notes 400 (5) 395
table: 2047 Notes 400 (9) 391
table: Total long-term debt $2,700 $(25) $2,675
table: At December 31, 2018
table: Gross Carrying Amount Unamortized Discount and Deferred Financing Costs Net Carrying Amount
table: 2021 Notes 650 (3) 647
table: 2022 Notes 400 (3) 397
table: 2026 Notes 850 (8) 842
table: 2027 Notes 400 (5) 395
table: 2047 Notes 400 (10) 390
table: Total long-term debt $2,700 $(29) $2,671
question: Analyse this data from a financial earnings document. What was the change in the gross carrying amount between the 2021 and 2022 Notes in 2019?