Investment Securities, Major Categories (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale securities:
Cost, available-for-sale securities	$ 241,635	$ 248,087
Gross unrealized gains, available-for-sale securities	9,049	9,071
Gross unrealized losses, available-for-sale securities	(2,433)	(5,151)
Fair value, available-for-sale securities	248,251	252,007
Held-to-maturity securities:
Cost, held-to-maturity securities	40,758	12,346
Gross unrealized gains, held-to-maturity securities	205	0
Gross unrealized losses, held-to-maturity securities	(48)	(99)
Fair value, held-to-maturity securities	40,915	12,247
Total investment securities:
Cost, investment securities	282,393	260,433
Gross unrealized gains, investment securities	9,254	9,071
Gross unrealized losses, investment securities	(2,481)	(5,250)
Fair value, investment securities	289,166	264,254
Total debt securities [Member]
Available-for-sale securities:
Cost, available-for-sale securities	239,705	246,048
Gross unrealized gains, available-for-sale securities	8,374	7,661
Gross unrealized losses, available-for-sale securities	(2,363)	(5,087)
Fair value, available-for-sale securities	245,716	248,622
Held-to-maturity securities:
Cost, held-to-maturity securities	40,758	12,346
Fair value, held-to-maturity securities	40,915	12,247
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Cost, available-for-sale securities	14,994	6,592
Gross unrealized gains, available-for-sale securities	12	17
Gross unrealized losses, available-for-sale securities	(212)	(329)
Fair value, available-for-sale securities	14,794	6,280
Held-to-maturity securities:
Cost, held-to-maturity securities	28,887
Gross unrealized gains, held-to-maturity securities	93
Gross unrealized losses, held-to-maturity securities	(42)
Fair value, held-to-maturity securities	28,938
Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Cost, available-for-sale securities	44,023	42,171
Gross unrealized gains, available-for-sale securities	2,000	1,092
Gross unrealized losses, available-for-sale securities	(218)	(727)
Fair value, available-for-sale securities	45,805	42,536
Held-to-maturity securities:
Cost, held-to-maturity securities	123
Gross unrealized gains, held-to-maturity securities	3
Gross unrealized losses, held-to-maturity securities	0
Fair value, held-to-maturity securities	126
Total mortgage-backed securities [Member]
Available-for-sale securities:
Cost, available-for-sale securities	137,184	148,052
Gross unrealized gains, available-for-sale securities	4,659	4,508
Gross unrealized losses, available-for-sale securities	(1,739)	(3,769)
Fair value, available-for-sale securities	140,104	148,791
Federal agencies [Member]
Available-for-sale securities:
Cost, available-for-sale securities	111,805	119,303
Gross unrealized gains, available-for-sale securities	2,478	1,902
Gross unrealized losses, available-for-sale securities	(1,670)	(3,614)
Fair value, available-for-sale securities	112,613	117,591
Held-to-maturity securities:
Cost, held-to-maturity securities	5,770	6,304
Gross unrealized gains, held-to-maturity securities	85	0
Gross unrealized losses, held-to-maturity securities	0	(99)
Fair value, held-to-maturity securities	5,855	6,205
Residential [Member]
Available-for-sale securities:
Cost, available-for-sale securities	8,848	11,060
Gross unrealized gains, available-for-sale securities	1,242	1,433
Gross unrealized losses, available-for-sale securities	(14)	(40)
Fair value, available-for-sale securities	10,076	12,453
Commercial [Member]
Available-for-sale securities:
Cost, available-for-sale securities	16,531	17,689
Gross unrealized gains, available-for-sale securities	939	1,173
Gross unrealized losses, available-for-sale securities	(55)	(115)
Fair value, available-for-sale securities	17,415	18,747
Corporate debt securities [Member]
Available-for-sale securities:
Cost, available-for-sale securities	15,550	20,391
Gross unrealized gains, available-for-sale securities	845	976
Gross unrealized losses, available-for-sale securities	(81)	(140)
Fair value, available-for-sale securities	16,314	21,227
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Cost, available-for-sale securities	21,520	19,610
Gross unrealized gains, available-for-sale securities	499	642
Gross unrealized losses, available-for-sale securities	(96)	(93)
Fair value, available-for-sale securities	21,923	20,159
Held-to-maturity securities:
Cost, held-to-maturity securities	1,404
Gross unrealized gains, held-to-maturity securities	1
Gross unrealized losses, held-to-maturity securities	(6)
Fair value, held-to-maturity securities	1,399
Other [Member]
Available-for-sale securities:
Cost, available-for-sale securities	6,434	9,232
Gross unrealized gains, available-for-sale securities	359	426
Gross unrealized losses, available-for-sale securities	(17)	(29)
Fair value, available-for-sale securities	6,776	9,629
Held-to-maturity securities:
Cost, held-to-maturity securities	4,574	6,042
Gross unrealized gains, held-to-maturity securities	23	0
Gross unrealized losses, held-to-maturity securities	0	0
Fair value, held-to-maturity securities	4,597	6,042
Total marketable equity securities [Member]
Available-for-sale securities:
Cost, available-for-sale securities	1,930	2,039
Gross unrealized gains, available-for-sale securities	675	1,410
Gross unrealized losses, available-for-sale securities	(70)	(64)
Fair value, available-for-sale securities	2,535	3,385
Perpetual preferred securities [Member]
Available-for-sale securities:
Cost, available-for-sale securities	1,625	1,703
Gross unrealized gains, available-for-sale securities	154	222
Gross unrealized losses, available-for-sale securities	(68)	(60)
Fair value, available-for-sale securities	1,711	1,865
Other marketable equity securities [Member]
Available-for-sale securities:
Cost, available-for-sale securities	305	336
Gross unrealized gains, available-for-sale securities	521	1,188
Gross unrealized losses, available-for-sale securities	(2)	(4)
Fair value, available-for-sale securities	$ 824	$ 1,520