Fair Value Measurements - Recurring Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 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	$ 37	$ 34	$ 46
Total gains or losses included in earnings	0	0	0	0
Total gains or losses included in other comprehensive income	0	0	0	0
Purchases and issuances	0	0	0	10
Sales and settlements	0	0	0	(19)
Transfers in and/or out of level 3	0	0	0	0
Balance at the end of the period	34	37	34	37
Change in unrealized gains or losses for the period included in earnings for securities held at the end of the reporting period	$ 0	$ 0	$ 0	$ 0