AFS and HTM Debt Securities, Contractual Maturities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 271,236	$ 269,912
Weighted average yield contractual maturities, Total, available-for-sale	3.62%
Due within 1 year, Contractual maturities, available-for-sale	$ 12,691
Percentage of weighted average yield, Due within 1 year, available-for-sale	2.10%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 13,689
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.08%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 21,705
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.58%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 223,151
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.75%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 153,179	144,788
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.97%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%
Due in 1-5 years, Contractual maturities, held-to-maturity, cost	$ 39,628
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.12%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 7,049
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.86%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 106,502
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	3.29%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 156,279	142,115
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	40,154
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	7,281
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	108,844
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 16,549	13,348
Weighted average yield contractual maturities, Total, available-for-sale	1.92%
Due within 1 year, Contractual maturities, available-for-sale	$ 10,035
Percentage of weighted average yield, Due within 1 year, available-for-sale	1.74%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 6,192
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.21%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 47
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	1.84%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 275
Percentage of weighted average yield, Due after 10 years, available-for-sale	2.25%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 44,774	44,751
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.12%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%
Due in 1-5 years, Contractual maturities, held-to-maturity, cost	$ 39,530
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.11%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 5,244
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.19%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	0.00%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 45,463	44,340
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	40,056
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	5,407
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	0
Securities of U.S. states and political subdivisions [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 40,503	49,264
Weighted average yield contractual maturities, Total, available-for-sale	4.84%
Due within 1 year, Contractual maturities, available-for-sale	$ 2,200
Percentage of weighted average yield, Due within 1 year, available-for-sale	3.01%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 4,455
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.32%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 4,240
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.36%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 29,608
Percentage of weighted average yield, Due after 10 years, available-for-sale	5.42%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 12,719	6,286
Weighted average yield contractual maturities, Total, held-to-maturity, cost	4.99%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%
Due in 1-5 years, Contractual maturities, held-to-maturity, cost	$ 83
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	6.02%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 1,756
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	4.86%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 10,880
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	5.00%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 13,022	6,200
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	83
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	1,825
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	11,114
Mortgage-backed securities [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 172,614	160,203
Weighted average yield contractual maturities, Total, available-for-sale	3.47%
Due within 1 year, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 152
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.37%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,883
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.75%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 170,579
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.48%
Federal agencies [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 167,535	153,203
Weighted average yield contractual maturities, Total, available-for-sale	3.47%
Due within 1 year, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 152
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.37%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,543
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.59%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 165,840
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.48%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 95,637	93,685
Weighted average yield contractual maturities, Total, held-to-maturity, cost	3.10%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%
Due in 1-5 years, Contractual maturities, held-to-maturity, cost	$ 15
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	3.53%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	0.00%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 95,622
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	3.10%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 97,745	91,509
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	15
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	0
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	97,730
Residential [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 853	2,775
Weighted average yield contractual maturities, Total, available-for-sale	2.88%
Due within 1 year, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	0.00%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	0.00%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 853
Percentage of weighted average yield, Due after 10 years, available-for-sale	2.88%
Commercial [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 4,226	4,225
Weighted average yield contractual maturities, Total, available-for-sale	3.57%
Due within 1 year, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	0.00%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 340
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.50%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 3,886
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.58%
Corporate debt securities [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 5,893	6,271
Weighted average yield contractual maturities, Total, available-for-sale	4.95%
Due within 1 year, Contractual maturities, available-for-sale	$ 452
Percentage of weighted average yield, Due within 1 year, available-for-sale	5.86%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 2,193
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	4.91%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 2,629
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	4.70%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 619
Percentage of weighted average yield, Due after 10 years, available-for-sale	5.50%
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 31,010	35,343
Weighted average yield contractual maturities, Total, available-for-sale	3.64%
Due within 1 year, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due within 1 year, available-for-sale	0.00%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 1
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	4.66%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 11,548
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.73%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 19,461
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.59%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 49	66
Weighted average yield contractual maturities, Total, held-to-maturity, cost	3.48%
Due within 1 year, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 1 year, held-to-maturity, cost	0.00%
Due in 1-5 years, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	0.00%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 49
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	3.48%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 0
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	0.00%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 49	66
Due within 1 year, Contractual maturities, held-to-maturity, fair value	0
Due in 1-5 years, Contractual maturities, held-to-maturity, fair value	0
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	49
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	0
Other [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 4,667	$ 5,483
Weighted average yield contractual maturities, Total, available-for-sale	2.82%
Due within 1 year, Contractual maturities, available-for-sale	$ 4
Percentage of weighted average yield, Due within 1 year, available-for-sale	5.10%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 696
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.49%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,358
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	1.96%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 2,609
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.09%