Accumulated Other Comprehensive Income - AOCI and Related Tax Effect (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in accumulated other comprehensive loss balances:
Other Comprehensive Income Other, Net of Tax, Portion Attributable to Parent	$ (1)	$ 0	$ 0
Before Tax Amount
Net change	(432)	91	(243)
Tax Effect
Net change	113	(39)	97
Net of Tax
Net change	(319)	52	(146)
Other Comprehensive Income Other Before Tax	(1)
Other Comprehensive Income Other Tax	0
Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax Amount
Other comprehensive income before reclassifications	(96)	(35)	(26)
Reclassifications	34	(69)	(167)
Net change	(62)	(104)	(193)
Tax Effect
Other comprehensive income before reclassifications	25	13	10
Reclassifications	(9)	25	68
Net change	16	38	78
Net of Tax
Other comprehensive income before reclassifications	(71)	(22)	(16)
Amounts reclassified from AOCI	25	(44)	(99)
Net change	(46)	(66)	(115)
Net Unrealized Gains (Losses) on Securities
Before Tax Amount
Net change	(190)	25	(90)
Tax Effect
Net change	50	(9)	34
Net of Tax
Other comprehensive income before reclassifications	(155)	15	(14)
Amounts reclassified from AOCI	15	1	(42)
Net change	(140)	16	(56)
Unrealized holding gains (losses) arising during the period on securities available for sale
Before Tax Amount
Other comprehensive income before reclassifications	(210)	24	(40)
Reclassifications	(8)	(17)	(69)
Tax Effect
Other comprehensive income before reclassifications	55	(9)	15
Reclassifications	2	7	27
Net of Tax
Other comprehensive income before reclassifications	(155)	15	(25)
Amounts reclassified from AOCI	(6)	(10)	(42)
Accretion of fair value adjustment on securities available for sale
Before Tax Amount
Other comprehensive income before reclassifications		(1)	(1)
Tax Effect
Other comprehensive income before reclassifications		0	0
Net of Tax
Other comprehensive income before reclassifications		(1)	(1)
Amortization of net unrealized (gains) losses on held to maturity securities
Before Tax Amount
Reclassifications	28	19	20
Tax Effect
Reclassifications	(7)	(7)	(8)
Net of Tax
Amounts reclassified from AOCI	21	12	12
Foreign Currency Translation Adjustment
Before Tax Amount
Net change	(3)	11	3
Tax Effect
Net change	1	(4)	(1)
Net of Tax
Other comprehensive income before reclassifications		7	2
Amounts reclassified from AOCI	0	0	0
Net change	(2)	7	2
Pension and Other Benefits Adjustment
Before Tax Amount
Net change	(176)	159	37
Tax Effect
Net change	46	(64)	(14)
Net of Tax
Other comprehensive income before reclassifications	(171)	69	(12)
Amounts reclassified from AOCI	41	26	35
Net change	(130)	95	23
Amortization of prior service credit
Before Tax Amount
Other comprehensive income before reclassifications	(41)	(48)	(30)
Tax Effect
Other comprehensive income before reclassifications	11	19	12
Net of Tax
Other comprehensive income before reclassifications	(30)	(29)	(18)
Recognized net actuarial gain (loss)
Before Tax Amount
Other comprehensive income before reclassifications	96	91	89
Tax Effect
Other comprehensive income before reclassifications	(25)	(36)	(35)
Net of Tax
Other comprehensive income before reclassifications	71	55	54
Pension and other benefits arising during the year
Before Tax Amount
Other comprehensive income before reclassifications	(231)	116	(20)
Tax Effect
Other comprehensive income before reclassifications	60	(47)	8
Net of Tax
Other comprehensive income before reclassifications	(171)	69	(12)
Net change
Before Tax Amount
Other comprehensive income before reclassifications			(2)
Tax Effect
Other comprehensive income before reclassifications			1
Net of Tax
Other comprehensive income before reclassifications			(1)
Accumulated Other Comprehensive Income (Loss)
Net of Tax
Other comprehensive income before reclassifications	(400)	69	(40)
Amounts reclassified from AOCI	81	(17)	(106)
Net change	$ (319)	$ 52	$ (146)