Investment Securities, Major Categories (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale securities:
Amortized Cost	$ 268,090	$ 310,153
Gross unrealized gains	3,692	3,618
Gross unrealized losses	(2,580)	(5,407)
Fair value	269,202	308,364
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	140,392	99,583
Gross unrealized gains	894	599
Gross unrealized losses	(896)	(1,027)
Held-to-maturity, at fair value	140,390	99,155
Total investment securities:
Amortized Cost	408,482	409,736
Gross unrealized gains	4,586	4,217
Gross unrealized losses	(3,476)	(6,434)
Fair value	409,592	407,519
Held-to-maturity, at fair value	140,390	99,155
Collateralized Debt Obligations [Member]
Available-for-sale securities:
Amortized Cost	923	819
Fair value	998	847
Asset-backed Securities, Securitized Loans and Receivables [Member]
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	345	1,300
Held-to-maturity, at fair value	345	1,300
Total investment securities:
Held-to-maturity, at fair value	345	1,300
Asset-backed Securities Collateralized by Dealer Floorplan Loans [Member]
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	500	1,100
Held-to-maturity, at fair value	501	1,100
Total investment securities:
Held-to-maturity, at fair value	501	1,100
Total debt securities [Member]
Available-for-sale securities:
Amortized Cost	267,476	309,447
Gross unrealized gains	3,271	3,102
Gross unrealized losses	(2,573)	(5,396)
Fair value	268,174	307,153
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	140,392	99,583
Held-to-maturity, at fair value	140,390	99,155
Total investment securities:
Held-to-maturity, at fair value	140,390	99,155
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Amortized Cost	17,950	25,874
Gross unrealized gains	11	54
Gross unrealized losses	(65)	(109)
Fair value	17,896	25,819
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	44,704	44,690
Gross unrealized gains	666	466
Gross unrealized losses	(35)	(77)
Held-to-maturity, at fair value	45,335	45,079
Total investment securities:
Held-to-maturity, at fair value	45,335	45,079
Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Amortized Cost	52,237	52,121
Gross unrealized gains	751	551
Gross unrealized losses	(975)	(1,571)
Fair value	52,013	51,101
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	6,325	6,336
Gross unrealized gains	60	17
Gross unrealized losses	(55)	(144)
Held-to-maturity, at fair value	6,330	6,209
Total investment securities:
Held-to-maturity, at fair value	6,330	6,209
Mortgage-backed securities: [Member]
Available-for-sale securities:
Amortized Cost	148,512	179,363
Gross unrealized gains	1,623	1,725
Gross unrealized losses	(1,425)	(3,540)
Fair value	148,710	177,548
Federal agencies [Member]
Available-for-sale securities:
Amortized Cost	136,336	163,513
Gross unrealized gains	1,009	1,175
Gross unrealized losses	(1,407)	(3,458)
Fair value	135,938	161,230
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	87,525	45,161
Gross unrealized gains	162	100
Gross unrealized losses	(806)	(804)
Held-to-maturity, at fair value	86,881	44,457
Total investment securities:
Held-to-maturity, at fair value	86,881	44,457
Residential [Member]
Available-for-sale securities:
Amortized Cost	6,829	7,375
Gross unrealized gains	532	449
Gross unrealized losses	(2)	(8)
Fair value	7,359	7,816
Commercial [Member]
Available-for-sale securities:
Amortized Cost	5,347	8,475
Gross unrealized gains	82	101
Gross unrealized losses	(16)	(74)
Fair value	5,413	8,502
Corporate debt securities [Member]
Available-for-sale securities:
Amortized Cost	9,261	11,186
Gross unrealized gains	424	381
Gross unrealized losses	(83)	(110)
Fair value	9,602	11,457
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Amortized Cost	33,168	34,764
Gross unrealized gains	298	287
Gross unrealized losses	(11)	(31)
Fair value	33,455	35,020
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	993	1,065
Gross unrealized gains	5	6
Gross unrealized losses	0	(1)
Held-to-maturity, at fair value	998	1,070
Total investment securities:
Held-to-maturity, at fair value	998	1,070
Other [Member]
Available-for-sale securities:
Amortized Cost	6,348	6,139
Gross unrealized gains	164	104
Gross unrealized losses	(14)	(35)
Fair value	6,498	6,208
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	845	2,331
Gross unrealized gains	1	10
Gross unrealized losses	0	(1)
Held-to-maturity, at fair value	846	2,340
Total investment securities:
Held-to-maturity, at fair value	846	2,340
Total marketable equity securities [Member]
Available-for-sale securities:
Amortized Cost	614	706
Gross unrealized gains	421	516
Gross unrealized losses	(7)	(11)
Fair value	1,028	1,211
Perpetual preferred securities [Member]
Available-for-sale securities:
Amortized Cost	446	445
Gross unrealized gains	23	35
Gross unrealized losses	(4)	(11)
Fair value	465	469
Other marketable equity securities [Member]
Available-for-sale securities:
Amortized Cost	168	261
Gross unrealized gains	398	481
Gross unrealized losses	(3)	0
Fair value	$ 563	$ 742