Capital - Actual Capital Amounts and Ratios for Commercial Bank in Comparison With Minimum Amounts and Ratios Required (Detail) - Bank - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Common Equity, Tier 1 Amount
Total regulatory capital, Common Equity, Tier 1 Amount	$ 5,217	$ 4,964
Minimum for capital adequacy purposes, Common Equity, Tier 1 Amount	1,964	1,834
Excess, Common Equity, Tier 1 Amount	$ 3,253	$ 3,130
Common Equity, Tier 1 Ratio
Total regulatory capital, Common Equity, Tier 1 Ratio	11.95%	12.18%
Minimum for capital adequacy purposes, Common Equity, Tier 1 Ratio	4.50%	4.50%
Excess, Common Equity, Tier 1 Ratio	7.45%	7.68%
Risk-Based Capital, Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	$ 5,217	$ 4,964
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	2,619	2,445
Excess, Risk-Based Capital, Tier 1 Amount	$ 2,598	$ 2,519
Risk-Based Capital, Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	11.95	12.18
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	6.00	6.00
Excess, Risk-Based Capital, Tier 1 Ratio	5.95	6.18
Risk-Based Capital, Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	$ 5,402	$ 5,145
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	3,491	3,260
Excess, Risk-Based Capital, Total Amount	$ 1,911	$ 1,885
Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	12.38	12.62
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00	8.00
Excess, Risk-Based Capital, Total Ratio	4.38	4.62
Leverage Capital, Amount
Total regulatory capital, Leverage Capital, Amount	$ 5,217	$ 4,964
Minimum for capital adequacy purposes, Leverage Capital, Amount	2,236	2,095
Excess, Leverage Capital, Amount	$ 2,981	$ 2,869
Leverage Capital, Ratio
Total regulatory capital, Leverage Capital, Ratio	9.33	9.48
Minimum for capital adequacy purposes, Leverage Capital, Ratio	4.00	4.00
Excess, Leverage Capital, Ratio	5.33	5.48