Investments (Summary of Investment Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Amortized cost
Held-to-maturity	$ 10,209	$ 10,382
Available-for-sale	11,452	11,759
Total HTM and AFS investment securities	21,661	22,141
Gross unrealized gains 1
Held-to-maturity	17	156
Available-for-sale	0	0
Total HTM and AFS investment securities	17	156
Gross unrealized losses
Held-to-maturity	121	72
Available-for-sale	1,521	1,459
Estimated fair value
Held-to-maturity, Estimated fair value	10,105	10,466
Available-for-sale	9,931	10,300
Total HTM and AFS investment securities	20,036	20,766
Total HTM and AFS investment securities	1,642	1,531
U.S. Treasury securities
Amortized cost
Available-for-sale	584	585
Gross unrealized gains 1
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	103	93
Estimated fair value
Available-for-sale	481	492
Agency securities
Amortized cost
Held-to-maturity	92	93
Available-for-sale	629	663
Gross unrealized gains 1
Held-to-maturity	0	0
Available-for-sale	0	0
Gross unrealized losses
Held-to-maturity	7	6
Available-for-sale	33	33
Estimated fair value
Held-to-maturity, Estimated fair value	85	87
Available-for-sale	596	630
Agency guaranteed mortgage-backed securities
Amortized cost
Held-to-maturity	9,776	9,935
Available-for-sale	8,335	8,530
Gross unrealized gains 1
Held-to-maturity	17	156
Available-for-sale	0	0
Gross unrealized losses
Held-to-maturity	97	50
Available-for-sale	1,282	1,239
Estimated fair value
Held-to-maturity, Estimated fair value	9,696	10,041
Available-for-sale	7,053	7,291
Small Business Administration loan-backed securities
Amortized cost
Available-for-sale	543	571
Gross unrealized gains 1
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	25	25
Estimated fair value
Available-for-sale	518	546
Municipal securities
Amortized cost
Held-to-maturity	341	354
Available-for-sale	1,336	1,385
Gross unrealized gains 1
Held-to-maturity	0	0
Available-for-sale	0	0
Gross unrealized losses
Held-to-maturity	17	16
Available-for-sale	77	67
Estimated fair value
Held-to-maturity, Estimated fair value	324	338
Available-for-sale	1,259	1,318
Other debt securities
Amortized cost
Available-for-sale	25	25
Gross unrealized gains 1
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	1	2
Estimated fair value
Available-for-sale	$ 24	23
Available-for-sale, Unrealized Gains, Other
Gross unrealized gains 1
Available-for-sale		$ 1