Investment Securities (Summary) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	$ 68,132	$ 63,514
Securities available for sale debt securities, unrealized gains	1,381	710
Securities available for sale debt securities, unrealized losses	(158)	(835)
Debt Securities, Available-for-sale	69,355	63,389
Held to Maturity Securities, Amortized Cost, Total	18,948	19,312
Held-to-maturity securities, unrealized gains	337	118
Held-to-maturity securities, unrealized losses	(86)	(411)
Held-to-maturity securities, fair value	19,199	19,019
US Treasury and Government [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	18,828	18,104
Securities available for sale debt securities, unrealized gains	371	133
Securities available for sale debt securities, unrealized losses	(17)	(137)
Debt Securities, Available-for-sale	19,182	18,100
Held to Maturity Securities, Amortized Cost, Total	767	758
Held-to-maturity securities, unrealized gains	53	28
Held-to-maturity securities, unrealized losses		(23)
Held-to-maturity securities, fair value	820	763
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	5,337	4,933
Securities available for sale debt securities, unrealized gains	89	59
Securities available for sale debt securities, unrealized losses	(7)	(20)
Debt Securities, Available-for-sale	5,419	4,972
Held to Maturity Securities, Amortized Cost, Total	170	182
Held-to-maturity securities, unrealized gains		1
Held-to-maturity securities, fair value	170	183
Other [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	3,169	3,821
Securities available for sale debt securities, unrealized gains	122	96
Securities available for sale debt securities, unrealized losses	(3)	(38)
Debt Securities, Available-for-sale	3,288	3,879
Held to Maturity Securities, Amortized Cost, Total	1,803	1,849
Held-to-maturity securities, unrealized gains	88	53
Held-to-maturity securities, unrealized losses	(18)	(28)
Held-to-maturity securities, fair value	1,873	1,874
Mortgage-backed Securities Agency [Member] \| Residential Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	33,508	29,413
Securities available for sale debt securities, unrealized gains	402	104
Securities available for sale debt securities, unrealized losses	(90)	(524)
Debt Securities, Available-for-sale	33,820	28,993
Held to Maturity Securities, Amortized Cost, Total	15,503	15,740
Held-to-maturity securities, unrealized gains	181	32
Held-to-maturity securities, unrealized losses	(68)	(358)
Held-to-maturity securities, fair value	15,616	15,414
Mortgage-backed Securities Agency [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	2,568	2,630
Securities available for sale debt securities, unrealized gains	47	13
Securities available for sale debt securities, unrealized losses	(30)	(66)
Debt Securities, Available-for-sale	2,585	2,577
Held to Maturity Securities, Amortized Cost, Total	95	143
Held-to-maturity securities, unrealized gains	3	1
Held-to-maturity securities, unrealized losses		(1)
Held-to-maturity securities, fair value	98	143
Mortgage-backed Securities Non-agency [Member] \| Residential Mortgage-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	1,745	1,924
Securities available for sale debt securities, unrealized gains	316	300
Securities available for sale debt securities, unrealized losses	(4)	(13)
Debt Securities, Available-for-sale	2,057	2,211
Held to Maturity Securities, Amortized Cost, Total	146	152
Held-to-maturity securities, unrealized gains	6	2
Held-to-maturity securities, fair value	152	154
Mortgage-backed Securities Non-agency [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale debt securities, amortized cost	2,977	2,689
Securities available for sale debt securities, unrealized gains	34	5
Securities available for sale debt securities, unrealized losses	(7)	(37)
Debt Securities, Available-for-sale	3,004	2,657
Held to Maturity Securities, Amortized Cost, Total	464	488
Held-to-maturity securities, unrealized gains	6	1
Held-to-maturity securities, unrealized losses		(1)
Held-to-maturity securities, fair value	$ 470	$ 488

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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