Accumulated Other Comprehensive Income - AOCI and Related Tax Effect (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in accumulated other comprehensive loss balances:
Other Comprehensive Income Other, Net of Tax, Portion Attributable to Parent	$ 1	$ (1)	$ 0
Before Tax Amount
Net change	626	(432)	91
Tax Effect
Net change	(164)	113	(39)
Net of Tax
Other comprehensive income before reclassifications	374	(400)	69
Amounts reclassified from AOCI	88	81	(17)
Net change	462	(319)	52
Other Comprehensive Income Other Before Tax	1	(1)
Other Comprehensive Income Other Tax	0	0
Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax Amount
Other comprehensive income before reclassifications	51	(96)	(35)
Reclassifications	91	34	(69)
Net change	142	(62)	(104)
Tax Effect
Other comprehensive income before reclassifications	(13)	25	13
Reclassifications	(24)	(9)	25
Net change	(37)	16	38
Net of Tax
Other comprehensive income before reclassifications	38	(71)	(22)
Amounts reclassified from AOCI	67	25	(44)
Net change	105	(46)	(66)
Net Unrealized Gains (Losses) on Securities
Before Tax Amount
Net change	379	(190)	25
Tax Effect
Net change	(99)	50	(9)
Net of Tax
Other comprehensive income before reclassifications	284	(155)	15
Amounts reclassified from AOCI	(4)	15	1
Net change	280	(140)	16
Unrealized holding gains (losses) arising during the period on securities available for sale
Before Tax Amount
Other comprehensive income before reclassifications	385	(210)	24
Reclassifications	(39)	(8)	(17)
Tax Effect
Other comprehensive income before reclassifications	(101)	55	(9)
Reclassifications	10	2	7
Net of Tax
Other comprehensive income before reclassifications	284	(155)	15
Amounts reclassified from AOCI	(29)	(6)	(10)
Accretion of fair value adjustment on securities available for sale
Before Tax Amount
Other comprehensive income before reclassifications			(1)
Tax Effect
Other comprehensive income before reclassifications			0
Net of Tax
Other comprehensive income before reclassifications			(1)
Amortization of net unrealized (gains) losses on held to maturity securities
Before Tax Amount
Reclassifications	33	28	19
Tax Effect
Reclassifications	(8)	(7)	(7)
Net of Tax
Amounts reclassified from AOCI	25	21	12
Foreign Currency Translation Adjustment
Before Tax Amount
Net change	0	(3)	11
Tax Effect
Net change	0	1	(4)
Net of Tax
Other comprehensive income before reclassifications		(2)
Amounts reclassified from AOCI	0	0	0
Net change	0	(2)	7
Pension and Other Benefits Adjustment
Before Tax Amount
Net change	104	(176)	159
Tax Effect
Net change	(28)	46	(64)
Net of Tax
Other comprehensive income before reclassifications	51	(171)	69
Amounts reclassified from AOCI	25	41	26
Net change	76	(130)	95
Amortization of prior service credit
Before Tax Amount
Other comprehensive income before reclassifications	(40)	(41)	(48)
Tax Effect
Other comprehensive income before reclassifications	11	11	19
Net of Tax
Other comprehensive income before reclassifications	(29)	(30)	(29)
Recognized net actuarial gain (loss)
Before Tax Amount
Other comprehensive income before reclassifications	74	96	91
Tax Effect
Other comprehensive income before reclassifications	(20)	(25)	(36)
Net of Tax
Other comprehensive income before reclassifications	54	71	55
Pension and other benefits arising during the year
Before Tax Amount
Other comprehensive income before reclassifications	70	(231)	116
Tax Effect
Other comprehensive income before reclassifications	(19)	60	(47)
Net of Tax
Other comprehensive income before reclassifications	51	(171)	69
Accumulated Other Comprehensive Income (Loss)
Net of Tax
Net change	$ 462	$ (319)	$ 52