Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	$ 3,494
Other comprehensive income (loss), net of tax	(1,711)	$ 2,531
AOCI ending balance	1,783
Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	2,186	935
Other comprehensive income (loss) before reclassifications	(1,145)	1,224
Amounts reclassified from AOCI into earnings	(3)	0
Other comprehensive income (loss), net of tax	(1,148)	1,224
AOCI ending balance	1,038	2,151
Hedging Relationships
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	1,362	354
Other comprehensive income (loss) before reclassifications	(338)	1,695
Amounts reclassified from AOCI into earnings	(243)	(321)
Other comprehensive income (loss), net of tax	(581)	1,374
AOCI ending balance	781	1,728
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(31)	(107)
Other comprehensive income (loss) before reclassifications	19	(67)
Amounts reclassified from AOCI into earnings	0	0
Other comprehensive income (loss), net of tax	19	(67)
AOCI ending balance	(12)	(174)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(23)	(26)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI into earnings	(1)	0
Other comprehensive income (loss), net of tax	(1)	0
AOCI ending balance	(24)	(26)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	3,494	1,156
Other comprehensive income (loss) before reclassifications	(1,464)	2,852
Amounts reclassified from AOCI into earnings	(247)	(321)
Other comprehensive income (loss), net of tax	(1,711)	2,531
AOCI ending balance	1,783	3,679
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Other comprehensive gain (loss)	$ (21)	142
Cumulative effects from adoption of new accounting standards | Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance		(8)
Cumulative effects from adoption of new accounting standards | Hedging Relationships
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance		0
Cumulative effects from adoption of new accounting standards | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance		0
Cumulative effects from adoption of new accounting standards | Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance		0
Cumulative effects from adoption of new accounting standards | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance		$ (8)