Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Loss Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 16,580	$ 18,355	$ 17,386
Other comprehensive income before reclassifications	374	(400)	69
Other Comprehensive Income (Loss), Net of Tax	462	(319)	52
Amounts reclassified from AOCI	88	81	(17)
Ending balance	16,367	16,580	18,355
Subtotal Before Tax Cut Jobs Act Reclassification			(844)
TaxCutsandJobsActReclassification			182
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(220)	(174)	(77)
Other comprehensive income before reclassifications	38	(71)	(22)
Other Comprehensive Income (Loss), Net of Tax	105	(46)	(66)
Amounts reclassified from AOCI	67	25	(44)
Ending balance	(115)	(220)	(174)
Subtotal Before Tax Cut Jobs Act Reclassification			(143)
TaxCutsandJobsActReclassification			31
Adjustments to Additional Paid in Capital, Other		0
Accumulated Net Investment Gain (Loss) Arising During the Period, Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications	284	(155)	15
Amounts reclassified from AOCI	(29)	(6)	(10)
Net Unrealized Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(373)	(233)	(208)
Other comprehensive income before reclassifications	284	(155)	15
Other Comprehensive Income (Loss), Net of Tax	280	(140)	16
Amounts reclassified from AOCI	(4)	15	1
Ending balance	(93)	(373)	(233)
Subtotal Before Tax Cut Jobs Act Reclassification			(192)
TaxCutsandJobsActReclassification			41
Adjustments to Additional Paid in Capital, Other		0
Foreign Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	(19)	(22)
Other comprehensive income before reclassifications		(2)
Other Comprehensive Income (Loss), Net of Tax	0	(2)	7
Amounts reclassified from AOCI	0	0	0
Ending balance	0	0	(19)
Subtotal Before Tax Cut Jobs Act Reclassification			(15)
TaxCutsandJobsActReclassification			4
Adjustments to Additional Paid in Capital, Other		21
Pension and Other Benefits Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(730)	(600)	(589)
Other comprehensive income before reclassifications	51	(171)	69
Other Comprehensive Income (Loss), Net of Tax	76	(130)	95
Amounts reclassified from AOCI	25	41	26
Ending balance	(654)	(730)	(600)
Subtotal Before Tax Cut Jobs Act Reclassification			(494)
TaxCutsandJobsActReclassification			106
Adjustments to Additional Paid in Capital, Other		0
Accumulated Other [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1)	0	0
Other comprehensive income before reclassifications	1	(1)	0
Amounts reclassified from AOCI	0	0	0
Ending balance	0	(1)	0
Subtotal Before Tax Cut Jobs Act Reclassification			0
TaxCutsandJobsActReclassification			0
Adjustments to Additional Paid in Capital, Other		0
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,324)	(1,026)	(896)
Other Comprehensive Income (Loss), Net of Tax	462	(319)	52
Ending balance	$ (862)	(1,324)	$ (1,026)
Adjustments to Additional Paid in Capital, Other		$ 21