Investment Securities (Summary) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 56,595	$ 59,906
Securities available for sale debt securities, unrealized gains	946	736
Securities available for sale debt securities, unrealized losses	(287)	(538)
Securities available for sale, fair value	57,254	60,104
Held to Maturity Securities, Amortized Cost, Total	17,740	15,843
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	56,059	59,303
Securities available for sale debt securities, unrealized gains	946	736
Securities available for sale debt securities, unrealized losses	(285)	(536)
Securities available for sale, fair value	56,720	59,503
Held to Maturity Securities, Amortized Cost, Total	17,740	15,843
Held-to-maturity securities, unrealized gains	285	220
Held-to-maturity securities, unrealized losses	(130)	(197)
Held-to-maturity securities, fair value	17,895	15,866
US Treasury and Government Agencies Securities [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	13,233	13,100
Securities available for sale debt securities, unrealized gains	193	151
Securities available for sale debt securities, unrealized losses	(42)	(77)
Securities available for sale, fair value	13,384	13,174
Held to Maturity Securities, Amortized Cost, Total	736	527
Held-to-maturity securities, unrealized gains	41	35
Held-to-maturity securities, unrealized losses	(12)	(22)
Held-to-maturity securities, fair value	765	540
Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Agency [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	25,744	26,245
Securities available for sale debt securities, unrealized gains	176	170
Securities available for sale debt securities, unrealized losses	(170)	(287)
Securities available for sale, fair value	25,750	26,128
Held to Maturity Securities, Amortized Cost, Total	13,509	11,074
Held-to-maturity securities, unrealized gains	106	68
Held-to-maturity securities, unrealized losses	(102)	(161)
Held-to-maturity securities, fair value	13,513	10,981
Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,642	3,191
Securities available for sale debt securities, unrealized gains	326	227
Securities available for sale debt securities, unrealized losses	(22)	(52)
Securities available for sale, fair value	2,946	3,366
Held to Maturity Securities, Amortized Cost, Total	174	191
Held-to-maturity securities, unrealized gains	6	7
Held-to-maturity securities, fair value	180	198
Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Agency [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,002	2,150
Securities available for sale debt securities, unrealized gains	4	3
Securities available for sale debt securities, unrealized losses	(29)	(34)
Securities available for sale, fair value	1,977	2,119
Held to Maturity Securities, Amortized Cost, Total	430	903
Held-to-maturity securities, unrealized gains	8	24
Held-to-maturity securities, fair value	438	927
Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,730	4,023
Securities available for sale debt securities, unrealized gains	28	29
Securities available for sale debt securities, unrealized losses	(7)	(27)
Securities available for sale, fair value	2,751	4,025
Held to Maturity Securities, Amortized Cost, Total	543	567
Held-to-maturity securities, unrealized gains	16	10
Held-to-maturity securities, fair value	559	577
Asset-backed Securities [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	5,283	5,938
Securities available for sale debt securities, unrealized gains	73	52
Securities available for sale debt securities, unrealized losses	(4)	(22)
Securities available for sale, fair value	5,352	5,968
Held to Maturity Securities, Amortized Cost, Total	355	558
Held-to-maturity securities, unrealized gains	1
Held-to-maturity securities, unrealized losses		(2)
Held-to-maturity securities, fair value	356	556
Other debt [Member] \| Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	4,425	4,656
Securities available for sale debt securities, unrealized gains	146	104
Securities available for sale debt securities, unrealized losses	(11)	(37)
Securities available for sale, fair value	4,560	4,723
Held to Maturity Securities, Amortized Cost, Total	1,993	2,023
Held-to-maturity securities, unrealized gains	107	76
Held-to-maturity securities, unrealized losses	(16)	(12)
Held-to-maturity securities, fair value	2,084	2,087
Corporate Stocks And Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale equity securities, amortized cost	536	603
Securities available for sale equity securities, unrealized losses	(2)	(2)
Securities available for sale equity securities, fair value	$ 534	$ 601

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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