Accumulated Other Comprehensive Income - AOCI and Related Tax Effect (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flow hedge activities:
Unrealized net gains (losses) on hedges arising during the period, Before Tax Amount	$ 195	$ 126	$ 29
Less: Reclassification adjustment for net (gains) losses on hedges included in interest income for loans and interest expense on long-term debt, Before Tax Amount	(170)	(117)	(43)
Net change, Before Tax Amount	25	9	(14)
Unrealized net gains (losses) on hedges arising during the period, Tax Effect	(77)	(50)	(11)
Less: Reclassification adjustment for net (gains) losses on hedges included in interest income for loans and interest expense on long-term debt, Tax Effect	67	46	17
Net change, Tax Effect	(10)	(4)	6
Unrealized net gains (losses) on hedges arising during the period, Net of Tax	118	76	18
Less: Reclassification adjustment for net (gains) losses on hedges included in interest income for loans and interest expense on long-term debt, Net of Tax	(103)	(71)	(26)
Net change, Net of Tax	15	5	(8)
Securities:
Unrealized holding gains (losses) arising during the period on securities available for sale, Before Tax Amount	(7)	348	(401)
Reclassification adjustment for net (gains) losses on securities available for sale included in securities gains, net, Before Tax Amount	(20)	(18)	(178)
Less: accretion of fair value adjustment on securities available for sale, Before Tax Amount	(4)	(48)	(75)
Less: accretion of fair value adjustment on held to maturity securities, Before Tax Amount			(12)
Less: amortization of net unrealized (gains) losses on held to maturity securities, Before Tax Amount	20	19	(137)
Net change, Before Tax Amount	(11)	301	(803)
Foreign currency translation adjustment, Before Tax Amount	(24)	(11)	(7)
Unrealized holding gains (losses) arising during the period on securities available for sale, Tax Effect	3	(136)	157
Reclassification adjustment for net (gains) losses on securities available for sale included in securities gains, net, Tax Effect	8	7	70
Less: accretion of fair value adjustment on securities available for sale, Tax Effect	2	19	30
Less: accretion of fair value adjustment on held to maturity securities, Tax Effect			5
Less: amortization of net unrealized (gains) losses on held to maturity securities, Tax Effect	(8)	(8)	54
Net change, Tax Effect	5	(118)	316
Foreign currency translation adjustment, Tax Effect	9	4	3
Unrealized holding gains (losses) arising during the period on securities available for sale, Net of Tax	(4)	212	(244)
Reclassification adjustment for net (gains) losses on securities available for sale included in securities gains, net, Net of Tax	(12)	(11)	(108)
Less: accretion of fair value adjustment on securities available for sale, Net of Tax	(2)	(29)	(45)
Less: accretion of fair value adjustment on held to maturity securities, Net of Tax			(7)
Less: amortization of net unrealized (gains) losses on held to maturity securities, Net of Tax	12	11	(83)
Net change, Net of Tax	(6)	183	(487)
Foreign currency translation adjustment, Net of Tax	(15)	(7)	(4)
Pension and other benefits:
Amortization of prior service costs, Before Tax Amount	(25)	(17)
Recognized net actuarial (gain) loss, Before Tax Amount	121	62	116
Pension and other benefits arising during the year, Before Tax Amount	(124)	(517)	526
Net change, Before Tax Amount	(28)	(472)	642
Net change in AOCI, Before Tax Amount	(38)	(173)	(182)
Amortization of prior service costs, Tax Effect	9	7
Recognized net actuarial (gain) loss, Tax Effect	(47)	(24)	(46)
Pension and other benefits arising during the year, Tax Effect	49	203	(207)
Net change, Tax Effect	11	186	(253)
Net change in AOCI, Tax Effect	15	68	72
Amortization of prior service costs, Net of Tax	(16)	(10)
Recognized net actuarial gain (loss), Net of Tax	74	38	70
Pension and other benefits arising during the year, Net of Tax	(75)	(314)	319
Net change, Net of Tax	(17)	(286)	389
Net change in AOCI, Net of Tax	$ (23)	$ (105)	$ (110)