Investments (Summary of Investment Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Amortized cost
Held-to-maturity	$ 10,961	$ 11,126
Available-for-sale	13,075	13,538
Total HTM and AFS investment securities	24,036	24,664
Gross unrealized gains
Held-to-maturity	281	165
Available-for-sale	1	2
Total HTM and AFS investment securities	282	167
Gross unrealized losses
Held-to-maturity	32	52
Available-for-sale	1,482	1,625
Estimated fair value
Held-to-maturity, Estimated fair value	11,210	11,239
Available-for-sale	11,594	11,915
Total HTM and AFS investment securities	22,804	23,154
Total HTM and AFS investment securities	1,514	1,677
Municipal securities
Amortized cost
Held-to-maturity	392	405
Available-for-sale	1,517	1,732
Gross unrealized gains
Held-to-maturity	0	0
Available-for-sale	0	1
Gross unrealized losses
Held-to-maturity	24	31
Available-for-sale	70	99
Estimated fair value
Held-to-maturity, Estimated fair value	368	374
Available-for-sale	1,447	1,634
U.S. Treasury securities
Amortized cost
Available-for-sale	656	557
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	145	164
Estimated fair value
Available-for-sale	511	393
Agency securities
Amortized cost
Held-to-maturity	98	100
Available-for-sale	753	782
Gross unrealized gains
Held-to-maturity	0	0
Available-for-sale	0	0
Gross unrealized losses
Held-to-maturity	6	7
Available-for-sale	37	46
Estimated fair value
Held-to-maturity, Estimated fair value	92	93
Available-for-sale	716	736
Agency guaranteed mortgage-backed securities
Amortized cost
Held-to-maturity	10,471	10,621
Available-for-sale	9,423	9,652
Gross unrealized gains
Held-to-maturity	281	165
Available-for-sale	0	0
Gross unrealized losses
Held-to-maturity	2	14
Available-for-sale	1,203	1,285
Estimated fair value
Held-to-maturity, Estimated fair value	10,750	10,772
Available-for-sale	8,220	8,367
Small Business Administration loan-backed securities
Amortized cost
Available-for-sale	701	740
Gross unrealized gains
Available-for-sale	1	1
Gross unrealized losses
Available-for-sale	26	29
Estimated fair value
Available-for-sale	676	712
Other debt securities
Amortized cost
Available-for-sale	25	75
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	1	2
Estimated fair value
Available-for-sale	$ 24	$ 73