Investment Securities, Major Categories (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale securities:
Amortized Cost	$ 254,930	$ 249,653
Gross unrealized gains	7,673	9,711
Gross unrealized losses	(1,936)	(1,922)
Fair value	260,667	257,442
Held-to-maturity securities:
Amortized Cost	80,102	55,483
Gross unrealized gains	706	897
Gross unrealized losses	(493)	(21)
Fair value	80,315	56,359
Total investment securities:
Amortized Cost	335,032	305,136
Gross unrealized gains	8,379	10,608
Gross unrealized losses	(2,429)	(1,943)
Fair value	340,982	313,801
Asset-backed Securities, Securitized Loans and Receivables [Member]
Held-to-maturity securities:
Amortized Cost	2,700	3,800
Fair value	2,700	3,800
Asset-backed Securities Collateralized by Dealer Floorplan Loans [Member]
Held-to-maturity securities:
Amortized Cost	1,600	1,900
Fair value	1,600	2,000
Total debt securities [Member]
Available-for-sale securities:
Amortized Cost	253,785	247,747
Gross unrealized gains	6,317	7,869
Gross unrealized losses	(1,922)	(1,850)
Fair value	258,180	253,766
Held-to-maturity securities:
Fair value	80,315	56,359
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Amortized Cost	35,945	25,898
Gross unrealized gains	127	44
Gross unrealized losses	(128)	(138)
Fair value	35,944	25,804
Held-to-maturity securities:
Amortized Cost	44,645	40,886
Gross unrealized gains	544	670
Gross unrealized losses	(97)	(8)
Fair value	45,092	41,548
Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Amortized Cost	47,736	43,939
Gross unrealized gains	1,158	1,504
Gross unrealized losses	(596)	(499)
Fair value	48,298	44,944
Held-to-maturity securities:
Amortized Cost	2,174	1,962
Gross unrealized gains	2	27
Gross unrealized losses	(26)	0
Fair value	2,150	1,989
Mortgage-backed securities: [Member]
Available-for-sale securities:
Amortized Cost	121,004	132,311
Gross unrealized gains	3,797	4,873
Gross unrealized losses	(953)	(832)
Fair value	123,848	136,352
Federal agencies [Member]
Available-for-sale securities:
Amortized Cost	98,542	107,850
Gross unrealized gains	2,424	2,990
Gross unrealized losses	(888)	(751)
Fair value	100,078	110,089
Held-to-maturity securities:
Amortized Cost	27,577	5,476
Gross unrealized gains	130	165
Gross unrealized losses	(369)	0
Fair value	27,338	5,641
Residential [Member]
Available-for-sale securities:
Amortized Cost	7,580	8,213
Gross unrealized gains	894	1,080
Gross unrealized losses	(13)	(24)
Fair value	8,461	9,269
Commercial [Member]
Available-for-sale securities:
Amortized Cost	14,882	16,248
Gross unrealized gains	479	803
Gross unrealized losses	(52)	(57)
Fair value	15,309	16,994
Corporate debt securities [Member]
Available-for-sale securities:
Amortized Cost	14,564	14,211
Gross unrealized gains	586	745
Gross unrealized losses	(176)	(170)
Fair value	14,974	14,786
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Amortized Cost	28,911	25,137
Gross unrealized gains	467	408
Gross unrealized losses	(55)	(184)
Fair value	29,323	25,361
Held-to-maturity securities:
Amortized Cost	1,405	1,404
Gross unrealized gains	3	0
Gross unrealized losses	(1)	(13)
Fair value	1,407	1,391
Other [Member]
Available-for-sale securities:
Amortized Cost	5,625	6,251
Gross unrealized gains	182	295
Gross unrealized losses	(14)	(27)
Fair value	5,793	6,519
Held-to-maturity securities:
Amortized Cost	4,301	5,755
Gross unrealized gains	27	35
Gross unrealized losses	0	0
Fair value	4,328	5,790
Total marketable equity securities [Member]
Available-for-sale securities:
Amortized Cost	1,145	1,906
Gross unrealized gains	1,356	1,842
Gross unrealized losses	(14)	(72)
Fair value	2,487	3,676
Perpetual preferred securities [Member]
Available-for-sale securities:
Amortized Cost	841	1,622
Gross unrealized gains	129	148
Gross unrealized losses	(12)	(70)
Fair value	958	1,700
Other marketable equity securities [Member]
Available-for-sale securities:
Amortized Cost	304	284
Gross unrealized gains	1,227	1,694
Gross unrealized losses	(2)	(2)
Fair value	$ 1,529	$ 1,976