Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Loss Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 18,355	$ 17,386	$ 16,593
Other Comprehensive Income (Loss), Net of Tax	(319)	52	(146)
Ending balance	16,580	18,355	17,386
Net Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(174)	(77)	38
Other comprehensive income before reclassifications	(71)	(22)	(16)
Other Comprehensive Income (Loss), Net of Tax	(46)	(66)	(115)
Amounts reclassified from AOCI	25	(44)	(99)
Ending balance	(220)	(174)	(77)
Subtotal Before Tax Cut Jobs Act Reclassification		(143)
TaxCutsandJobsActReclassification		(31)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	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	(155)	15	(25)
Amounts reclassified from AOCI	(6)	(10)	(42)
TaxCutsandJobsActReclassification		(41)
Net Unrealized Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(233)	(208)	(152)
Other comprehensive income before reclassifications	(155)	15	(14)
Other Comprehensive Income (Loss), Net of Tax	(140)	16	(56)
Amounts reclassified from AOCI	15	1	(42)
Ending balance	(373)	(233)	(208)
Subtotal Before Tax Cut Jobs Act Reclassification		(192)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0
Foreign Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(19)	(22)	(24)
Other comprehensive income before reclassifications		7	2
Other Comprehensive Income (Loss), Net of Tax	(2)	7	2
Amounts reclassified from AOCI	0	0	0
Ending balance	0	(19)	(22)
Subtotal Before Tax Cut Jobs Act Reclassification		(15)
TaxCutsandJobsActReclassification		(4)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	21
Pension and Other Benefits Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(600)	(589)	(612)
Other comprehensive income before reclassifications	(171)	69	(12)
Other Comprehensive Income (Loss), Net of Tax	(130)	95	23
Amounts reclassified from AOCI	41	26	35
Ending balance	(730)	(600)	(589)
Subtotal Before Tax Cut Jobs Act Reclassification		(494)
TaxCutsandJobsActReclassification		(106)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0
Accumulated Other [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications	(1)
Amounts reclassified from AOCI	0
Ending balance	(1)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,026)	(896)	(750)
Other comprehensive income before reclassifications	(400)	69	(40)
Other Comprehensive Income (Loss), Net of Tax	(319)	52	(146)
Amounts reclassified from AOCI	81	(17)	(106)
Ending balance	(1,324)	(1,026)	$ (896)
Subtotal Before Tax Cut Jobs Act Reclassification		(844)
TaxCutsandJobsActReclassification		$ (182)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	$ 21