Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	$ 239	$ 624	$ (813)	$ 2,290
Other comprehensive income (loss), tax effect	(57)	(150)	186	(531)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	22,595	21,873	23,111	21,203
Other comprehensive (loss) income, net of tax	182	474	(627)	1,759
Ending Balance	22,926	22,335	22,926	22,335
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	306	602	(609)	1,757
Other comprehensive income (loss), before reclassifications, tax effect	(71)	(146)	143	(419)
Other comprehensive income (loss), before reclassifications, net activity	235	456	(466)	1,338
Reclassification adjustment, pre-tax activity	(7)		9
Reclassification adjustment, tax effect	2		(2)
Reclassification adjustment, net activity	(5)		7
Other comprehensive income (loss), pre-tax activity	299	602	(600)	1,757
Other comprehensive income (loss), tax effect	(69)	(146)	141	(419)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,242	1,694	1,931	812
Other comprehensive (loss) income, net of tax	230	456	(459)	1,338
Ending Balance	1,472	2,150	1,472	2,150
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	11	83	(70)	624
Other comprehensive income (loss), before reclassifications, tax effect	(2)	(17)	15	(131)
Other comprehensive income (loss), before reclassifications, net activity	9	66	(55)	493
Reclassification adjustment, pre-tax activity	(73)	(62)	(146)	(94)
Reclassification adjustment, tax effect	15	13	31	20
Reclassification adjustment, net activity	(58)	(49)	(115)	(74)
Other comprehensive income (loss), pre-tax activity	(62)	21	(216)	530
Other comprehensive income (loss), tax effect	13	(4)	46	(111)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	597	824	718	422
Other comprehensive (loss) income, net of tax	(49)	17	(170)	419
Ending Balance	548	841	548	841
Defined benefit pension plans, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(1)		(1)
Other comprehensive income (loss), before reclassifications, tax effect	0		0
Other comprehensive income (loss), before reclassifications, net activity	(1)		(1)
Reclassification adjustment, pre-tax activity	3	1	4	3
Reclassification adjustment, tax effect	(1)	0	(1)	(1)
Reclassification adjustment, net activity	2	1	3	2
Other comprehensive income (loss), pre-tax activity	2	1	3	3
Other comprehensive income (loss), tax effect	(1)	0	(1)	(1)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(43)	(41)	(44)	(42)
Other comprehensive (loss) income, net of tax	1	1	2	2
Ending Balance	(42)	(40)	(42)	(40)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	0		0
Other comprehensive income (loss), tax effect	0		0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(4)		(4)
Other comprehensive (loss) income, net of tax	0		0
Ending Balance	(4)		(4)
AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,792	2,477	2,601	1,192
Ending Balance	$ 1,974	$ 2,951	$ 1,974	$ 2,951