Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	$ (1,053)	$ 1,665
Other comprehensive income (loss), tax effect	244	(380)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	23,111	21,203
Other comprehensive (loss) income, net of tax	(809)	1,285
Ending Balance	22,595	21,873
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(914)	1,155
Other comprehensive income (loss), before reclassifications, tax effect	214	(273)
Other comprehensive income (loss), before reclassifications, net activity	(700)	882
Reclassification adjustment, pre-tax activity	15
Reclassification adjustment, tax effect	(4)
Reclassification adjustment, net activity	11
Other comprehensive income (loss), pre-tax activity	(899)	1,155
Other comprehensive income (loss), tax effect	210	(273)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,931	812
Other comprehensive (loss) income, net of tax	(689)	882
Ending Balance	1,242	1,694
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(84)	541
Other comprehensive income (loss), before reclassifications, tax effect	20	(114)
Other comprehensive income (loss), before reclassifications, net activity	(64)	427
Reclassification adjustment, pre-tax activity	(72)	(32)
Reclassification adjustment, tax effect	15	7
Reclassification adjustment, net activity	(57)	(25)
Other comprehensive income (loss), pre-tax activity	(156)	509
Other comprehensive income (loss), tax effect	35	(107)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	718	422
Other comprehensive (loss) income, net of tax	(121)	402
Ending Balance	597	824
Defined benefit pension plans, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, pre-tax activity	2	1
Reclassification adjustment, tax effect	(1)	0
Reclassification adjustment, net activity	1	1
Other comprehensive income (loss), pre-tax activity	2	1
Other comprehensive income (loss), tax effect	(1)	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(44)	(42)
Other comprehensive (loss) income, net of tax	1	1
Ending Balance	(43)	(41)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	0
Other comprehensive income (loss), tax effect	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(4)
Other comprehensive (loss) income, net of tax	0
Ending Balance	(4)
AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	2,601	1,192
Ending Balance	$ 1,792	$ 2,477