Securities - Distribution of Maturities of Debt Securities with Approximate Yield of Portfolio (Detail) $ in Millions	Dec. 31, 2024 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 3,040
Available-for-sale yield within one year (percent)	0.83%
Available-for-sale amount after one but within five years	$ 6,381
Available-for-sale yield after one but within five years (percent)	3.62%
Available-for-sale amount after five but within ten years	$ 2,877
Available-for-sale yield after five but within ten years (percent)	3.82%
Available-for-sale amount after ten years	$ 14,923
Available-for-sale yield after ten years (percent)	2.63%
Total fair value within one year	$ 3,032
Total fair value after one but within five years	6,339
Total fair value after five but within ten years	2,855
Total fair value after ten years	12,711
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	$ 2,542
Held-to-maturity yield after one but within five years (percent)	3.57%
Held-to-maturity after five but within ten years	$ 1,092
Held-to-maturity yield after five but within ten years (percent)	3.75%
Held-to-maturity after ten years	$ 14,164
Held-to-maturity yield after ten years (percent)	4.55%
Total fair value within one year	$ 0
Total fair value after one but within five years	2,472
Total fair value after five but within ten years	1,021
Total fair value after ten years	13,536
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 866
Available-for-sale yield within one year (percent)	1.27%
Available-for-sale amount after one but within five years	$ 4,782
Available-for-sale yield after one but within five years (percent)	3.38%
Available-for-sale amount after five but within ten years	$ 2,277
Available-for-sale yield after five but within ten years (percent)	4.17%
Available-for-sale amount after ten years	$ 2,325
Available-for-sale yield after ten years (percent)	3.04%
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	$ 2,323
Held-to-maturity yield after one but within five years (percent)	3.64%
Held-to-maturity after five but within ten years	$ 484
Held-to-maturity yield after five but within ten years (percent)	3.77%
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	$ 177
Available-for-sale yield within one year (percent)	1.74%
Available-for-sale amount after one but within five years	$ 125
Available-for-sale yield after one but within five years (percent)	3.50%
Available-for-sale amount after five but within ten years	$ 429
Available-for-sale yield after five but within ten years (percent)	1.89%
Available-for-sale amount after ten years	$ 4,565
Available-for-sale yield after ten years (percent)	1.81%
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	$ 217
Held-to-maturity yield after one but within five years (percent)	2.84%
Held-to-maturity after five but within ten years	$ 597
Held-to-maturity yield after five but within ten years (percent)	3.70%
Held-to-maturity after ten years	$ 351
Held-to-maturity yield after ten years (percent)	2.87%
U.S. Government agency issued or guaranteed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 20
Available-for-sale yield within one year (percent)	0.81%
Available-for-sale amount after one but within five years	$ 0
Available-for-sale yield after one but within five years (percent)	0.00%
Available-for-sale amount after five but within ten years	$ 2
Available-for-sale yield after five but within ten years (percent)	4.85%
Available-for-sale amount after ten years	$ 8,022
Available-for-sale yield after ten years (percent)	2.97%
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	$ 11
Held-to-maturity yield after five but within ten years (percent)	6.04%
Held-to-maturity after ten years	$ 13,813
Held-to-maturity yield after ten years (percent)	4.59%
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
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	$ 2
Held-to-maturity yield after one but within five years (percent)	3.79%
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	$ 51
Available-for-sale yield after one but within five years (percent)	4.40%
Available-for-sale amount after five but within ten years	$ 47
Available-for-sale yield after five but within ten years (percent)	3.91%
Available-for-sale amount after ten years	$ 11
Available-for-sale yield after ten years (percent)	4.50%
Foreign debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale amount within one year	$ 1,977
Available-for-sale yield within one year (percent)	0.56%
Available-for-sale amount after one but within five years	$ 1,423
Available-for-sale yield after one but within five years (percent)	4.41%
Available-for-sale amount after five but within ten years	$ 122
Available-for-sale yield after five but within ten years (percent)	4.01%
Available-for-sale amount after ten years	$ 0
Available-for-sale yield after ten years (percent)	0.00%