Investments (Summary of Investment Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Amortized cost
Held-to-maturity	$ 441	$ 636
Available-for-sale	24,202	15,417
Total debt investment securities	24,643	16,053
Gross unrealized gains
Available-for-sale	170	370
Total HTM and AFS investment securities	174	375
Gross unrealized losses
Available-for-sale	324	56
Total HTM and AFS investment securities	326	57
Estimated fair value
Held-to-maturity	443	640
Available-for-sale	24,048	15,731
Total HTM and AFS investment securities	24,491	16,371
Municipal securities
Amortized cost
Held-to-maturity	441	636
Available-for-sale	1,652	1,352
Gross unrealized gains
Held-to-maturity	4	5
Available-for-sale	46	68
Gross unrealized losses
Held-to-maturity	2	1
Available-for-sale	4	0
Estimated fair value
Held-to-maturity	443	640
Available-for-sale	1,694	1,420
U.S. Treasury securities
Amortized cost
Available-for-sale	155	205
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	21	13
Estimated fair value
Available-for-sale	134	192
Agency securities
Amortized cost
Available-for-sale	833	1,051
Gross unrealized gains
Available-for-sale	13	40
Gross unrealized losses
Available-for-sale	1	0
Estimated fair value
Available-for-sale	845	1,091
Agency guaranteed mortgage-backed securities
Amortized cost
Available-for-sale	20,549	11,439
Gross unrealized gains
Available-for-sale	108	262
Gross unrealized losses
Available-for-sale	270	8
Estimated fair value
Available-for-sale	20,387	11,693
Small Business Administration loan-backed securities
Amortized cost
Available-for-sale	938	1,195
Gross unrealized gains
Available-for-sale	2	0
Gross unrealized losses
Available-for-sale	28	35
Estimated fair value
Available-for-sale	912	1,160
Other debt securities
Amortized cost
Available-for-sale	75	175
Gross unrealized gains
Available-for-sale	1	0
Gross unrealized losses
Available-for-sale	0	0
Estimated fair value
Available-for-sale	$ 76	$ 175