Fair Value Measurements - Recurring Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reconciliation of items measured at fair value on a recurring basis that used significant unobservable inputs (Level 3)
Balance at the beginning of the period	$ 34	$ 46
Total gains or losses included in earnings	0	0
Total gains or losses included in other comprehensive income	0	0
Purchases and issuances	0	10
Sales and settlements	0	(19)
Transfers in and/or out of Level 3	0	0
Balance at the end of the period	34	37
Total gains or losses included in other comprehensive income	$ 0	$ 0