Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	$ 1,836	$ 1,696	$ (246)
Other comprehensive income (loss), tax effect	(427)	(392)	63
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	21,203	16,250	16,220
Other comprehensive income (loss), net of tax	1,409	1,304	(183)
Ending balance	23,111	21,203	16,250
Net unrealized gains on available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	1,514	1,369	(483)
Other comprehensive income (loss), before reclassifications, tax effect	(361)	(323)	112
Other comprehensive income (loss), before reclassifications, net activity	1,153	1,046	(371)
Reclassification adjustment, pre-tax activity	(45)	(9)	11
Reclassification adjustment, tax effect	11	2	(2)
Reclassification adjustment, net activity	(34)	(7)	9
Other comprehensive income (loss), pre-tax activity	1,469	1,360	(472)
Other comprehensive income (loss), tax effect	(350)	(321)	110
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	812	(227)	135
Other comprehensive income (loss), net of tax	1,119	1,039	(362)
Ending balance	1,931	812	(227)
Net unrealized gains on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	611	348	214
Other comprehensive income (loss), before reclassifications, tax effect	(128)	(73)	(45)
Other comprehensive income (loss), before reclassifications, net activity	483	275	169
Reclassification adjustment, pre-tax activity	(237)	(16)	2
Reclassification adjustment, tax effect	50	3	0
Reclassification adjustment, net activity	(187)	(13)	2
Other comprehensive income (loss), pre-tax activity	374	332	216
Other comprehensive income (loss), tax effect	(78)	(70)	(45)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	422	160	(11)
Other comprehensive income (loss), net of tax	296	262	171
Ending balance	718	422	160
Defined benefit pension plans, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(12)	(5)	1
Other comprehensive income (loss), before reclassifications, tax effect	3	0	0
Other comprehensive income (loss), before reclassifications, net activity	(9)	(5)	1
Reclassification adjustment, pre-tax activity	9	9	9
Reclassification adjustment, tax effect	(2)	(1)	(2)
Reclassification adjustment, net activity	7	8	7
Other comprehensive income (loss), pre-tax activity	(3)	4	10
Other comprehensive income (loss), tax effect	1	(1)	(2)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(42)	(45)	(53)
Other comprehensive income (loss), net of tax	(2)	3	8
Ending balance	(44)	(42)	(45)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	(4)
Other comprehensive income (loss), tax effect	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0
Other comprehensive income (loss), net of tax	(4)
Ending balance	(4)	0
AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,192	(112)	71
Ending balance	$ 2,601	$ 1,192	$ (112)