Securities - Distribution of Maturities of Debt Securities with Approximate Yield of Portfolio (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 2,137
Available-for-sale yield within one year (percent)	0.35%
Available-for-sale amount after one but within five years	$ 6,227
Available-for-sale yield after one but within five years (percent)	2.31%
Available-for-sale amount after five but within ten years	$ 2,044
Available-for-sale yield after five but within ten years (percent)	2.03%
Available-for-sale amount after ten years	$ 17,572
Available-for-sale yield after ten years (percent)	2.56%
Total fair value within one year	$ 2,113
Total fair value after one but within five years	6,121
Total fair value after five but within ten years	1,940
Total fair value after ten years	15,522
Held-to-maturity amount within one year	$ 87
Held-to-maturity yield within one year (percent)	2.35%
Held-to-maturity amount after one but within five years	$ 1,179
Held-to-maturity yield after one but within five years (percent)	3.74%
Held-to-maturity after five but within ten years	$ 1,621
Held-to-maturity yield after five but within ten years (percent)	3.58%
Held-to-maturity after ten years	$ 12,189
Held-to-maturity yield after ten years (percent)	4.41%
Total fair value within one year	$ 85
Total fair value after one but within five years	1,170
Total fair value after five but within ten years	1,563
Total fair value after ten years	11,871
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 0
Available-for-sale yield within one year (percent)	0.00%
Available-for-sale amount after one but within five years	$ 3,910
Available-for-sale yield after one but within five years (percent)	1.61%
Available-for-sale amount after five but within ten years	$ 632
Available-for-sale yield after five but within ten years (percent)	1.51%
Available-for-sale amount after ten years	$ 2,947
Available-for-sale yield after ten years (percent)	2.70%
Held-to-maturity amount within one year	$ 0
Held-to-maturity yield within one year (percent)	0.00%
Held-to-maturity amount after one but within five years	$ 1,095
Held-to-maturity yield after one but within five years (percent)	3.75%
Held-to-maturity after five but within ten years	$ 822
Held-to-maturity yield after five but within ten years (percent)	3.71%
Held-to-maturity after ten years	$ 0
Held-to-maturity yield after ten years (percent)	0.00%
U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 803
Available-for-sale yield within one year (percent)	0.98%
Available-for-sale amount after one but within five years	$ 1,055
Available-for-sale yield after one but within five years (percent)	2.56%
Available-for-sale amount after five but within ten years	$ 1,362
Available-for-sale yield after five but within ten years (percent)	2.20%
Available-for-sale amount after ten years	$ 5,799
Available-for-sale yield after ten years (percent)	1.84%
Held-to-maturity amount within one year	$ 86
Held-to-maturity yield within one year (percent)	2.31%
Held-to-maturity amount after one but within five years	$ 81
Held-to-maturity yield after one but within five years (percent)	3.64%
Held-to-maturity after five but within ten years	$ 786
Held-to-maturity yield after five but within ten years (percent)	3.41%
Held-to-maturity after ten years	$ 413
Held-to-maturity yield after ten years (percent)	2.91%
U.S. Government agency issued or guaranteed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 0
Available-for-sale yield within one year (percent)	0.00%
Available-for-sale amount after one but within five years	$ 69
Available-for-sale yield after one but within five years (percent)	3.16%
Available-for-sale amount after five but within ten years	$ 2
Available-for-sale yield after five but within ten years (percent)	5.97%
Available-for-sale amount after ten years	$ 8,813
Available-for-sale yield after ten years (percent)	2.98%
Held-to-maturity amount within one year	$ 0
Held-to-maturity yield within one year (percent)	0.00%
Held-to-maturity amount after one but within five years	$ 0
Held-to-maturity yield after one but within five years (percent)	0.00%
Held-to-maturity after five but within ten years	$ 12
Held-to-maturity yield after five but within ten years (percent)	5.75%
Held-to-maturity after ten years	$ 11,776
Held-to-maturity yield after ten years (percent)	4.46%
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Held-to-maturity amount within one year	$ 1
Held-to-maturity yield within one year (percent)	5.14%
Held-to-maturity amount after one but within five years	$ 3
Held-to-maturity yield after one but within five years (percent)	2.73%
Held-to-maturity after five but within ten years	$ 0
Held-to-maturity yield after five but within ten years (percent)	0.00%
Held-to-maturity after ten years	$ 0
Held-to-maturity yield after ten years (percent)	0.00%
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 0
Available-for-sale yield within one year (percent)	0.00%
Available-for-sale amount after one but within five years	$ 55
Available-for-sale yield after one but within five years (percent)	4.38%
Available-for-sale amount after five but within ten years	$ 48
Available-for-sale yield after five but within ten years (percent)	3.90%
Available-for-sale amount after ten years	$ 13
Available-for-sale yield after ten years (percent)	5.64%
Held-to-maturity amount within one year	$ 0
Held-to-maturity yield within one year (percent)	0.00%
Held-to-maturity amount after one but within five years	$ 0
Held-to-maturity yield after one but within five years (percent)	0.00%
Held-to-maturity after five but within ten years	$ 1
Held-to-maturity yield after five but within ten years (percent)	4.44%
Held-to-maturity after ten years	$ 0
Held-to-maturity yield after ten years (percent)	0.00%
Foreign debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 1,334
Available-for-sale yield within one year (percent)	(0.03%)
Available-for-sale amount after one but within five years	$ 1,138
Available-for-sale yield after one but within five years (percent)	4.34%
Available-for-sale amount after five but within ten years	$ 0
Available-for-sale yield after five but within ten years (percent)	0.00%
Available-for-sale amount after ten years	$ 0
Available-for-sale yield after ten years (percent)	0.00%