Investment Securities, Contractual Maturities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 268,174	$ 307,153
Weighted average yield contractual maturities, Total, available-for-sale	3.60%	3.44%
Due within 1 year, Contractual maturities, available-for-sale	$ 13,329	$ 6,418
Percentage of weighted average yield, Due within 1 year, available-for-sale	1.40%	1.93%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 20,441	$ 37,442
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.88%	2.20%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 33,455	$ 31,202
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.15%	3.17%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 200,949	$ 232,091
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.90%	3.72%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 140,392	$ 99,583
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	140,390	99,155
Total debt securities [Member]
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 140,392	$ 99,583
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.92%	2.87%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 33,186	$ 33,663
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.04%	2.04%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 13,933	$ 14,883
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.52%	2.43%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 93,273	$ 51,037
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	3.29%	3.55%
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	$ 140,390	$ 99,155
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	33,644	34,025
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	14,118	14,918
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	92,628	50,212
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 17,896	$ 25,819
Weighted average yield contractual maturities, Total, available-for-sale	1.25%	1.44%
Due within 1 year, Contractual maturities, available-for-sale	$ 10,987	$ 1,328
Percentage of weighted average yield, Due within 1 year, available-for-sale	1.04%	0.92%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 5,883	$ 23,477
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	1.55%	1.45%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,026	$ 1,014
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	1.80%	1.80%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 0	$ 0
Percentage of weighted average yield, Due after 10 years, available-for-sale	0.00%	0.00%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 44,704	$ 44,690
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.12%	2.12%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 32,317	$ 31,956
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.04%	2.05%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 12,387	$ 12,734
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.32%	2.30%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	$ 45,335	$ 45,079
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	32,774	32,313
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	12,561	12,766
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	0	0
Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 52,013	$ 51,101
Weighted average yield contractual maturities, Total, available-for-sale	5.77%	5.65%
Due within 1 year, Contractual maturities, available-for-sale	$ 1,251	$ 2,990
Percentage of weighted average yield, Due within 1 year, available-for-sale	2.25%	1.69%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 10,536	$ 9,299
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.86%	2.74%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 2,511	$ 2,391
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	4.59%	4.71%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 37,715	$ 36,421
Percentage of weighted average yield, Due after 10 years, available-for-sale	6.78%	6.78%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 6,325	$ 6,336
Weighted average yield contractual maturities, Total, held-to-maturity, cost	6.04%	6.04%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 24	$ 24
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	8.20%	8.20%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 553	$ 436
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	6.61%	6.76%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 5,748	$ 5,876
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	5.98%	5.98%
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	$ 6,330	$ 6,209
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	24	24
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	559	430
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	5,747	5,755
Mortgage-backed securities: [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 148,710	$ 177,548
Weighted average yield contractual maturities, Total, available-for-sale	3.25%	3.19%
Due within 1 year, Contractual maturities, available-for-sale	$ 1	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	4.93%	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 152	$ 153
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.42%	3.34%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 5,909	$ 5,428
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.93%	3.16%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 142,648	$ 171,967
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.27%	3.19%
Federal agencies [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 135,938	$ 161,230
Weighted average yield contractual maturities, Total, available-for-sale	3.18%	3.09%
Due within 1 year, Contractual maturities, available-for-sale	$ 1	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	4.93%	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 127	$ 128
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.01%	2.98%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 5,845	$ 5,363
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.93%	3.16%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 129,965	$ 155,739
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.19%	3.09%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 87,525	$ 45,161
Weighted average yield contractual maturities, Total, held-to-maturity, cost	3.11%	3.23%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 0	$ 0
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	0.00%	0.00%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	0.00%	0.00%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 87,525	$ 45,161
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	3.11%	3.23%
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	$ 86,881	$ 44,457
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	0	0
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	0	0
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	86,881	44,457
Residential [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 7,359	$ 7,816
Weighted average yield contractual maturities, Total, available-for-sale	3.90%	3.84%
Due within 1 year, Contractual maturities, available-for-sale	$ 0	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 25	$ 25
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	5.55%	5.21%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 19	$ 35
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.76%	4.34%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 7,315	$ 7,756
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.89%	3.83%
Commercial [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 5,413	$ 8,502
Weighted average yield contractual maturities, Total, available-for-sale	4.18%	4.58%
Due within 1 year, Contractual maturities, available-for-sale	$ 0	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 0	$ 0
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	0.00%	0.00%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 45	$ 30
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.90%	3.13%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 5,368	$ 8,472
Percentage of weighted average yield, Due after 10 years, available-for-sale	4.19%	4.59%
Corporate debt securities [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 9,602	$ 11,457
Weighted average yield contractual maturities, Total, available-for-sale	4.95%	4.81%
Due within 1 year, Contractual maturities, available-for-sale	$ 1,050	$ 2,043
Percentage of weighted average yield, Due within 1 year, available-for-sale	4.13%	2.90%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 2,945	$ 3,374
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	5.69%	5.89%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 4,638	$ 4,741
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	4.62%	4.71%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 969	$ 1,299
Percentage of weighted average yield, Due after 10 years, available-for-sale	5.23%	5.38%
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 33,455	$ 35,020
Weighted average yield contractual maturities, Total, available-for-sale	2.89%	2.70%
Due within 1 year, Contractual maturities, available-for-sale	$ 0	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 146	$ 168
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.10%	1.34%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 17,739	$ 16,482
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.82%	2.66%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 15,570	$ 18,370
Percentage of weighted average yield, Due after 10 years, available-for-sale	2.99%	2.74%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 993	$ 1,065
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.72%	2.58%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 0	$ 0
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	0.00%	0.00%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 993	$ 1,065
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.72%	2.58%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	$ 998	$ 1,070
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	0	0
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	998	1,070
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	0	0
Other [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 6,498	$ 6,208
Weighted average yield contractual maturities, Total, available-for-sale	2.32%	2.18%
Due within 1 year, Contractual maturities, available-for-sale	$ 40	$ 57
Percentage of weighted average yield, Due within 1 year, available-for-sale	3.24%	3.06%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 779	$ 971
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.54%	2.35%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,632	$ 1,146
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	1.91%	2.04%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 4,047	$ 4,034
Percentage of weighted average yield, Due after 10 years, available-for-sale	2.43%	2.17%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 845	$ 2,331
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.03%	1.83%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 845	$ 1,683
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.03%	1.81%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 0	$ 648
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	0.00%	1.89%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 0	$ 0
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	0.00%	0.00%
Held-to-maturity securities, fair value: [Abstract]
Contractual maturities, Total amount, held-to-maturity, fair value	$ 846	$ 2,340
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	846	1,688
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	0	652
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	$ 0	$ 0