Securities - Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	$ 37,178	$ 32,830
Available-for-sale debt securities, unrealized losses	(12)	(464)
Available-for-sale debt securities, unrealized gains	1,528	166
Available-for-sale debt securities, amortized cost	35,662	33,128
Held-to-maturity securities, fair value	18	18
Held-to-maturity, unrealized losses	0	0
Held-to-maturity, unrealized gains	0	0
Held-to-maturity securities, amortized cost	18	18
Trading debt securities, fair value	297	287
Equity securities, fair value	459	452
U.S. Treasury and federal agency
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	75	97
Available-for-sale debt securities, unrealized losses	0	(1)
Available-for-sale debt securities, unrealized gains	1	0
Available-for-sale debt securities, amortized cost	74	98
Obligations of states and political subdivisions
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	2	2
Available-for-sale debt securities, unrealized losses	0	0
Available-for-sale debt securities, unrealized gains	0	0
Available-for-sale debt securities, amortized cost	2	2
Held-to-maturity securities, fair value	16	16
Held-to-maturity, unrealized losses	0	0
Held-to-maturity, unrealized gains	0	0
Held-to-maturity securities, amortized cost	16	16
Agency mortgage-backed securities \| Residential mortgage backed securities
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	15,694	16,247
Available-for-sale debt securities, unrealized losses	(1)	(242)
Available-for-sale debt securities, unrealized gains	510	86
Available-for-sale debt securities, amortized cost	15,185	16,403
Agency mortgage-backed securities \| Commercial mortgage backed securities
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	15,276	10,650
Available-for-sale debt securities, unrealized losses	(1)	(164)
Available-for-sale debt securities, unrealized gains	826	44
Available-for-sale debt securities, amortized cost	14,451	10,770
Non-agency mortgage-backed securities \| Commercial mortgage backed securities
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	3,400	3,267
Available-for-sale debt securities, unrealized losses	0	(47)
Available-for-sale debt securities, unrealized gains	154	9
Available-for-sale debt securities, amortized cost	3,246	3,305
Asset-backed securities and other debt securities
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	2,156	2,015
Available-for-sale debt securities, unrealized losses	(10)	(10)
Available-for-sale debt securities, unrealized gains	37	27
Available-for-sale debt securities, amortized cost	2,129	1,998
Held-to-maturity securities, fair value	2	2
Held-to-maturity, unrealized losses	0	0
Held-to-maturity, unrealized gains	0	0
Held-to-maturity securities, amortized cost	2	2
Other securities
Investment Holdings [Line Items]
Available-for-sale debt securities, fair value	575	552
Available-for-sale debt securities, unrealized losses	0	0
Available-for-sale debt securities, unrealized gains	0	0
Available-for-sale debt securities, amortized cost	$ 575	$ 552

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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