The fair value of our Senior Notes was determined using quoted prices in active markets for identical securities, which are considered Level 1 inputs. The fair value of our Senior Notes due 2021 was $631 million and $620 million as of September 30, 2019 and December 31, 2018, respectively. The fair value of our Senior Notes due 2023 was $583 million and $599 million as of September 30, 2019 and December 31, 2018, respectively. The fair value of our Senior Notes due 2026 was $515 million and $476 million as of September 30, 2019 and December 31, 2018, respectively. The fair value of our Senior Notes due 2046 was $455 million and $397 million as of September 30, 2019 and December 31, 2018, respectively.

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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