Investment Securities (Summary) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 57,212	$ 59,906
Securities available for sale debt securities, unrealized gains	854	736
Securities available for sale debt securities, unrealized losses	(448)	(538)
Securities available for sale, fair value	57,618	60,104
Held to Maturity Securities, Amortized Cost, Total	18,513	15,843
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	56,625	59,303
Securities available for sale debt securities, unrealized gains	854	736
Securities available for sale debt securities, unrealized losses	(446)	(536)
Securities available for sale, fair value	57,033	59,503
Held to Maturity Securities, Amortized Cost, Total	18,513	15,843
Held-to-maturity securities, unrealized gains	224	220
Held-to-maturity securities, unrealized losses	(172)	(197)
Held-to-maturity securities, fair value	18,565	15,866
US Treasury and Government Agencies Securities \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	14,432	13,100
Securities available for sale debt securities, unrealized gains	173	151
Securities available for sale debt securities, unrealized losses	(84)	(77)
Securities available for sale, fair value	14,521	13,174
Held to Maturity Securities, Amortized Cost, Total	741	527
Held-to-maturity securities, unrealized gains	37	35
Held-to-maturity securities, unrealized losses	(13)	(22)
Held-to-maturity securities, fair value	765	540
Residential mortgage-backed Securities \| Mortgage-backed Securities Agency \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	25,534	26,245
Securities available for sale debt securities, unrealized gains	121	170
Securities available for sale debt securities, unrealized losses	(249)	(287)
Securities available for sale, fair value	25,406	26,128
Held to Maturity Securities, Amortized Cost, Total	14,503	11,074
Held-to-maturity securities, unrealized gains	77	68
Held-to-maturity securities, unrealized losses	(139)	(161)
Held-to-maturity securities, fair value	14,441	10,981
Residential mortgage-backed Securities \| Mortgage-backed Securities Non-agency \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,443	3,191
Securities available for sale debt securities, unrealized gains	336	227
Securities available for sale debt securities, unrealized losses	(21)	(52)
Securities available for sale, fair value	2,758	3,366
Held to Maturity Securities, Amortized Cost, Total	167	191
Held-to-maturity securities, unrealized gains	7	7
Held-to-maturity securities, fair value	174	198
Commercial Mortgage Backed Securities \| Mortgage-backed Securities Agency \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	1,960	2,150
Securities available for sale debt securities, unrealized gains	2	3
Securities available for sale debt securities, unrealized losses	(58)	(34)
Securities available for sale, fair value	1,904	2,119
Held to Maturity Securities, Amortized Cost, Total	407	903
Held-to-maturity securities, unrealized gains	4	24
Held-to-maturity securities, fair value	411	927
Commercial Mortgage Backed Securities \| Mortgage-backed Securities Non-agency \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,603	4,023
Securities available for sale debt securities, unrealized gains	19	29
Securities available for sale debt securities, unrealized losses	(9)	(27)
Securities available for sale, fair value	2,613	4,025
Held to Maturity Securities, Amortized Cost, Total	538	567
Held-to-maturity securities, unrealized gains	10	10
Held-to-maturity securities, fair value	548	577
Asset-backed Securities \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	5,331	5,938
Securities available for sale debt securities, unrealized gains	74	52
Securities available for sale debt securities, unrealized losses	(8)	(22)
Securities available for sale, fair value	5,397	5,968
Held to Maturity Securities, Amortized Cost, Total	200	558
Held-to-maturity securities, unrealized gains	1
Held-to-maturity securities, unrealized losses		(2)
Held-to-maturity securities, fair value	201	556
Other debt \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	4,322	4,656
Securities available for sale debt securities, unrealized gains	129	104
Securities available for sale debt securities, unrealized losses	(17)	(37)
Securities available for sale, fair value	4,434	4,723
Held to Maturity Securities, Amortized Cost, Total	1,957	2,023
Held-to-maturity securities, unrealized gains	88	76
Held-to-maturity securities, unrealized losses	(20)	(12)
Held-to-maturity securities, fair value	2,025	2,087
Corporate Stocks And Other
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale equity securities, fair value	585	601
Securities available for sale equity securities, unrealized losses	(2)	(2)
Securities available for sale equity securities, amortized cost	$ 587	$ 603

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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