Derivative Financial Instruments - Derivative Notional Values (Detail) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Total Derivative Notional Values	$ 54,500,000,000	$ 61,300,000,000
Designated as Hedging Instrument [Member] | Cash Flow [Member]
Derivative [Line Items]
Total Derivative Notional Values	11,400,000,000	12,100,000,000
Designated as Hedging Instrument [Member] | Fair Value [Member]
Derivative [Line Items]
Total Derivative Notional Values	8,200,000,000	8,300,000,000
Trading [Member]
Derivative [Line Items]
Total Derivative Notional Values	34,900,000,000	40,900,000,000
Interest Rate Swaps [Member]
Derivative [Line Items]
Total Derivative Notional Values	44,400,000,000	46,700,000,000
Interest Rate Swaps [Member] | Designated as Hedging Instrument [Member] | Cash Flow [Member]
Derivative [Line Items]
Total Derivative Notional Values	11,400,000,000	12,100,000,000
Interest Rate Swaps [Member] | Designated as Hedging Instrument [Member] | Fair Value [Member]
Derivative [Line Items]
Total Derivative Notional Values	6,200,000,000	6,200,000,000
Interest Rate Swaps [Member] | Trading [Member]
Derivative [Line Items]
Total Derivative Notional Values	26,800,000,000	28,400,000,000
Floor Income Contracts [Member]
Derivative [Line Items]
Total Derivative Notional Values	8,100,000,000	12,500,000,000
Floor Income Contracts [Member] | Trading [Member]
Derivative [Line Items]
Total Derivative Notional Values	8,100,000,000	12,500,000,000
Cross-Currency Interest Rate Swaps [Member]
Derivative [Line Items]
Total Derivative Notional Values	2,000,000,000.0	2,100,000,000
Cross-Currency Interest Rate Swaps [Member] | Designated as Hedging Instrument [Member] | Fair Value [Member]
Derivative [Line Items]
Total Derivative Notional Values	$ 2,000,000,000.0	$ 2,100,000,000