Securities - Maturity Distribution and Yield of Investment Securities Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Securities available-for-sale, Amount:
One year or less	$ 19,377
Over 1 through 5 years	28,132
Over 5 through 10 years	10,739
Over 10 years	3,991
Total	110,067	$ 88,550
Securities held-to-maturity, Amount:
One year or less	3,545
Over 1 through 5 years	5,406
Over 5 through 10 years	243
Over 10 years	497
Amortized cost	44,615	34,483
Mortgage-backed securities
Securities available-for-sale, Amount:
Without single maturity date	40,653
Securities held-to-maturity, Amount:
Mortgage-backed securities	34,924
Asset-backed securities
Securities available-for-sale, Amount:
Without single maturity date	7,175
U.S. Treasury
Securities available-for-sale, Amount:
One year or less	5,348
Over 1 through 5 years	10,350
Over 5 through 10 years	6,171
Over 10 years	3,268
Total	$ 25,137	15,431
Securities available-for-sale (Yield):
One year or less	0.50%
Over 1 through 5 years	1.52%
Over 5 through 10 years	1.67%
Over 10 years	3.11%
Total	1.54%
Securities held-to-maturity, Amount:
One year or less	$ 1,899
Over 1 through 5 years	2,788
Over 5 through 10 years	0
Over 10 years	0
Amortized cost	$ 4,687	3,818
Securities held-to-maturity (Yield):
One year or less	0.41%
Over 1 through 5 years	1.91%
Over 5 through 10 years	0.00%
Over 10 years	0.00%
Total	1.32%
U.S. government agencies
Securities available-for-sale, Amount:
One year or less	$ 25
Over 1 through 5 years	1,038
Over 5 through 10 years	1,623
Over 10 years	120
Total	$ 2,806	1,949
Securities available-for-sale (Yield):
One year or less	2.55%
Over 1 through 5 years	1.22%
Over 5 through 10 years	2.56%
Over 10 years	2.06%
Total	2.04%
Securities held-to-maturity, Amount:
One year or less	$ 0
Over 1 through 5 years	1,696
Over 5 through 10 years	212
Over 10 years	441
Amortized cost	$ 2,349	1,023
Securities held-to-maturity (Yield):
One year or less	0.00%
Over 1 through 5 years	1.12%
Over 5 through 10 years	1.98%
Over 10 years	2.33%
Total	1.42%
State and political subdivisions
Securities available-for-sale, Amount:
One year or less	$ 178
Over 1 through 5 years	646
Over 5 through 10 years	107
Over 10 years	248
Total	$ 1,179	1,044
Securities available-for-sale (Yield):
One year or less	2.92%
Over 1 through 5 years	3.29%
Over 5 through 10 years	2.42%
Over 10 years	2.37%
Total	2.96%
Securities held-to-maturity, Amount:
One year or less	$ 0
Over 1 through 5 years	3
Over 5 through 10 years	0
Over 10 years	13
Amortized cost	$ 16	$ 17
Securities held-to-maturity (Yield):
One year or less	0.00%
Over 1 through 5 years	5.66%
Over 5 through 10 years	0.00%
Over 10 years	4.76%
Total	4.91%
Other bonds, notes and debentures
Securities available-for-sale, Amount:
One year or less	$ 13,826
Over 1 through 5 years	16,098
Over 5 through 10 years	2,838
Over 10 years	355
Total	$ 33,117
Securities available-for-sale (Yield):
One year or less	0.71%
Over 1 through 5 years	0.68%
Over 5 through 10 years	0.53%
Over 10 years	0.97%
Total	0.69%
Securities held-to-maturity, Amount:
One year or less	$ 1,646
Over 1 through 5 years	919
Over 5 through 10 years	31
Over 10 years	43
Amortized cost	$ 2,639
Securities held-to-maturity (Yield):
One year or less	1.21%
Over 1 through 5 years	0.66%
Over 5 through 10 years	0.92%
Over 10 years	0.35%
Total	1.00%
Mortgage/ asset-backed
Securities available-for-sale, Amount:
Total	$ 47,828
Securities available-for-sale (Yield):
Total	2.23%
Securities held-to-maturity, Amount:
Amortized cost	$ 34,924
Securities held-to-maturity (Yield):
Total	2.87%
Mortgage/ asset-backed | Mortgage-backed securities
Securities available-for-sale, Amount:
Without single maturity date	$ 40,653
Securities available-for-sale (Yield):
Without single maturity date	2.24%
Securities held-to-maturity, Amount:
Mortgage-backed securities	$ 34,924
Securities held-to-maturity (Yield):
Without single maturity date	2.87%
Mortgage/ asset-backed | Asset-backed securities
Securities available-for-sale, Amount:
Without single maturity date	$ 7,175
Securities available-for-sale (Yield):
Without single maturity date	2.18%