Summary of Basis of Presentation and Recent Accounting Standards - Components of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 16,949		$ 19,123	$ 17,985	$ 19,123	$ 14,145
Other comprehensive income	52	$ 4	103	(111)	159	(327)
Balance at end of period	13,455	16,949		17,992	13,455	17,992
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(263)	(267)	(370)	(240)	(370)	(24)
Other comprehensive income	52			(111)	159	(327)
Balance at end of period	(211)	(263)	(267)	$ (351)	(211)	$ (351)
Unrealized Gains on Available-for-Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(263)	(267)	(362)		(362)
Other comprehensive income	52	4	95
Balance at end of period	(211)	(263)	(267)		(211)
Net Unrealized Gains on Derivatives Designated As Hedging Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	0	0	(8)		(8)
Other comprehensive income	0	0	8
Balance at end of period	$ 0	$ 0	$ 0		$ 0