AFS and HTM Debt Securities, Contractual Maturities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 265,983	$ 269,912
Weighted average yield contractual maturities, Total, available-for-sale	3.73%
Due within 1 year, Contractual maturities, available-for-sale	$ 8,033
Percentage of weighted average yield, Due within 1 year, available-for-sale	2.38%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 18,160
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.96%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 20,546
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.75%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 219,244
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.85%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 145,876	144,788
Weighted average yield contractual maturities, Total, held-to-maturity, cost	2.91%
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	$ 34,757
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.08%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 11,726
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.64%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 99,393
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	3.24%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 147,864	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	35,052
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	12,056
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	100,756
Securities of U.S. Treasury and federal agencies [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 15,319	13,348
Weighted average yield contractual maturities, Total, available-for-sale	1.94%
Due within 1 year, Contractual maturities, available-for-sale	$ 5,521
Percentage of weighted average yield, Due within 1 year, available-for-sale	1.69%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 9,747
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	2.08%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 51
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	1.89%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 0
Percentage of weighted average yield, Due after 10 years, available-for-sale	0.00%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 44,766	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	$ 34,667
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	2.07%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 10,099
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	2.28%
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	$ 45,336	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	34,962
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	10,374
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	$ 45,095	49,264
Weighted average yield contractual maturities, Total, available-for-sale	4.92%
Due within 1 year, Contractual maturities, available-for-sale	$ 2,016
Percentage of weighted average yield, Due within 1 year, available-for-sale	3.34%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 5,135
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.34%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 4,322
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.54%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 33,622
Percentage of weighted average yield, Due after 10 years, available-for-sale	5.40%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 7,948	6,286
Weighted average yield contractual maturities, Total, held-to-maturity, cost	4.97%
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	$ 75
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	6.05%
Due in 5-10 years, Contractual maturities, held-to-maturity, cost	$ 1,570
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	4.89%
Due in 10 years or more, Contractual maturities, held-to-maturity, cost	$ 6,303
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	4.98%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 8,125	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	75
Due in 5-10 years, Contractual maturities, held-to-maturity, fair value	1,625
Due in 10 years or more, Contractual maturities, held-to-maturity, fair value	6,425
Mortgage-backed securities [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 161,301	160,203
Weighted average yield contractual maturities, Total, available-for-sale	3.50%
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	$ 137
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.48%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 2,007
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.74%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 159,157
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.51%
Federal agencies [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 155,858	153,203
Weighted average yield contractual maturities, Total, available-for-sale	3.50%
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	$ 137
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.48%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,665
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.56%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 154,056
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.51%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 93,105	93,685
Weighted average yield contractual maturities, Total, held-to-maturity, cost	3.12%
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	$ 15
Percentage of weighted average yield, Due In 1-5 years, held-to-maturity, cost	3.77%
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	$ 93,090
Percentage of weighted average yield, Due after 10 years, held-to-maturity, cost	3.12%
Held-to-maturity securities, fair value:
Contractual maturities, Total amount, held-to-maturity, fair value	$ 94,346	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	94,331
Residential [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 1,263	2,775
Weighted average yield contractual maturities, Total, available-for-sale	2.80%
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	$ 1,263
Percentage of weighted average yield, Due after 10 years, available-for-sale	2.80%
Commercial [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 4,180	4,225
Weighted average yield contractual maturities, Total, available-for-sale	3.71%
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	$ 342
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	3.61%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 3,838
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.72%
Corporate debt securities [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 6,230	6,271
Weighted average yield contractual maturities, Total, available-for-sale	5.01%
Due within 1 year, Contractual maturities, available-for-sale	$ 484
Percentage of weighted average yield, Due within 1 year, available-for-sale	6.17%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 2,384
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	5.00%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 2,737
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	4.69%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 625
Percentage of weighted average yield, Due after 10 years, available-for-sale	5.59%
Collateralized loan and other debt obligations [Member]
Available-for-sale securities:
Contractual maturities, Total amount, available-for-sale	$ 32,995	35,343
Weighted average yield contractual maturities, Total, available-for-sale	3.96%
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	$ 8
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	5.02%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 10,005
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	4.03%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 22,982
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.93%
Held-to-maturity securities:
Held-to-maturity securities, Amortized Cost	$ 57	66
Weighted average yield contractual maturities, Total, held-to-maturity, cost	3.78%
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	$ 57
Percentage of weighted average yield, Due In 5-10 years, held-to-maturity, cost	3.78%
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	$ 57	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	57
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	$ 5,043	$ 5,483
Weighted average yield contractual maturities, Total, available-for-sale	3.10%
Due within 1 year, Contractual maturities, available-for-sale	$ 12
Percentage of weighted average yield, Due within 1 year, available-for-sale	3.34%
Due in 1-5 years, Contractual maturities, available-for-sale	$ 749
Percentage of weighted average yield, Due in 1-5 years, available-for-sale	3.80%
Due in 5-10 years, Contractual maturities, available-for-sale	$ 1,424
Percentage of weighted average yield, Due In 5-10 years, available-for-sale	2.13%
Due in 10 years or more, Contractual maturities, available-for-sale	$ 2,858
Percentage of weighted average yield, Due after 10 years, available-for-sale	3.40%