Fair Value Measurements - Changes in Fair Value Level 3 (Details) - Recurring measurement - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	$ 3	$ 372
Transfer in from Level 2	136
Net gains recognized in income	48	89
Purchases	101
Transfer out of Level 3	(246)
Sales		(458)
Other	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	$ 41	$ 3