Investment Securities (Summary) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost			$ 57,212
Securities available for sale debt securities, unrealized gains			854
Securities available for sale debt securities, unrealized losses			(448)
Securities available for sale, fair value	$ 56,018		57,618
Held to Maturity Securities, Amortized Cost, Total	18,544		18,513
Securities reclassified to equity investments	105		106
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale equity securities, amortized cost			587
Securities available for sale equity securities, unrealized losses			(2)
Securities available for sale equity securities, fair value			585
Accounting Standards Update 2016-01 [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities reclassified to equity investments	600	$ 600
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	56,241		56,625
Securities available for sale debt securities, unrealized gains	714		854
Securities available for sale debt securities, unrealized losses	(937)		(446)
Securities available for sale, fair value	56,018		57,033
Held to Maturity Securities, Amortized Cost, Total	18,544		18,513
Held-to-maturity securities, unrealized gains	115		224
Held-to-maturity securities, unrealized losses	(436)		(172)
Held-to-maturity securities, fair value	18,223		18,565
Debt Securities [Member] \| US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	13,645		14,432
Securities available for sale debt securities, unrealized gains	123		173
Securities available for sale debt securities, unrealized losses	(179)		(84)
Securities available for sale, fair value	13,589		14,521
Held to Maturity Securities, Amortized Cost, Total	745		741
Held-to-maturity securities, unrealized gains	28		37
Held-to-maturity securities, unrealized losses	(27)		(13)
Held-to-maturity securities, fair value	746		765
Debt Securities [Member] \| Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	26,512		25,534
Securities available for sale debt securities, unrealized gains	74		121
Securities available for sale debt securities, unrealized losses	(584)		(249)
Securities available for sale, fair value	26,002		25,406
Held to Maturity Securities, Amortized Cost, Total	14,663		14,503
Held-to-maturity securities, unrealized gains	18		77
Held-to-maturity securities, unrealized losses	(382)		(139)
Held-to-maturity securities, fair value	14,299		14,441
Debt Securities [Member] \| Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,320		2,443
Securities available for sale debt securities, unrealized gains	333		336
Securities available for sale debt securities, unrealized losses	(17)		(21)
Securities available for sale, fair value	2,636		2,758
Held to Maturity Securities, Amortized Cost, Total	163		167
Held-to-maturity securities, unrealized gains	3		7
Held-to-maturity securities, fair value	166		174
Debt Securities [Member] \| Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	1,884		1,960
Securities available for sale debt securities, unrealized gains	1		2
Securities available for sale debt securities, unrealized losses	(78)		(58)
Securities available for sale, fair value	1,807		1,904
Held to Maturity Securities, Amortized Cost, Total	338		407
Held-to-maturity securities, unrealized gains	2		4
Held-to-maturity securities, unrealized losses	(1)
Held-to-maturity securities, fair value	339		411
Debt Securities [Member] \| Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,585		2,603
Securities available for sale debt securities, unrealized gains	9		19
Securities available for sale debt securities, unrealized losses	(24)		(9)
Securities available for sale, fair value	2,570		2,613
Held to Maturity Securities, Amortized Cost, Total	524		538
Held-to-maturity securities, unrealized gains	4		10
Held-to-maturity securities, fair value	528		548
Debt Securities [Member] \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	5,129		5,331
Securities available for sale debt securities, unrealized gains	71		74
Securities available for sale debt securities, unrealized losses	(17)		(8)
Securities available for sale, fair value	5,183		5,397
Held to Maturity Securities, Amortized Cost, Total	196		200
Held-to-maturity securities, unrealized gains	1		1
Held-to-maturity securities, fair value	197		201
Debt Securities [Member] \| Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	4,166		4,322
Securities available for sale debt securities, unrealized gains	103		129
Securities available for sale debt securities, unrealized losses	(38)		(17)
Securities available for sale, fair value	4,231		4,434
Held to Maturity Securities, Amortized Cost, Total	1,915		1,957
Held-to-maturity securities, unrealized gains	59		88
Held-to-maturity securities, unrealized losses	(26)		(20)
Held-to-maturity securities, fair value	$ 1,948		$ 2,025

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