Derivatives and Hedging Fair Value of Derivative Contracts (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 16, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	$ 285.0	$ 38.0	$ 78.0
Derivative Liability, Fair Value	(237.0)	(96.0)	(135.0)
Derivative Asset, Not Subject to Master Netting Arrangement	30.0	12.0	19.0
Derivative Liability, Not Subject to Master Netting Arrangement	(44.0)	(4.0)	(6.0)
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	82.0	22.0	31.0
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	315.0	50.0	97.0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	11.0	(6.0)	(37.0)
Derivative Liability, Subject to Master Netting Arrangement, Asset Offset	233.0	28.0	66.0
Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	48.0	72.0	75.0
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	281.0	100.0	141.0
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(100.0)	(1.0)	(1.0)
Derivative Asset, Subject to Master Netting Arrangement, Liability Offset	(233.0)	(28.0)	(66.0)
Derivative Asset, Subject to Master Netting Arrangement, after Offset	52.0	10.0	12.0
Derivative Liability, Subject to Master Netting Arrangement, after Offset	4.0	68.0	69.0
Subordinated Debentures Maturing July 2056 [Member] | Subordinated Debt [Member]
Derivatives, Fair Value [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.25%
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	22.0	14.0	7.0
Derivative Liability, Fair Value	0.0	(54.0)	(57.0)
Derivative Asset, Not Subject to Master Netting Arrangement	5.0	0.0	0.0
Derivative Liability, Not Subject to Master Netting Arrangement	(5.0)	0.0	0.0
Derivative Netting Adjustments, Liabilities	0.0	0.0	0.0
Derivative Netting Adjustments, Assets	0.0	0.0	0.0
Derivative Asset, Subject to Master Netting Arrangement, after Offset	22.0	14.0	7.0
Derivative Liability, Subject to Master Netting Arrangement, after Offset	0.0	54.0	57.0
Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Not Subject to Master Netting Arrangement	2.0	0.0	2.0
Derivative Liability, Not Subject to Master Netting Arrangement	(1.0)	(2.0)	0.0
Interest Rate Lock Commitments
Derivatives, Fair Value [Line Items]
Derivative Asset, Not Subject to Master Netting Arrangement	3.0	11.0	15.0
Derivative Liability, Not Subject to Master Netting Arrangement	(31.0)	(2.0)	(6.0)
Forward purchase contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	3.0	8.0	1.0
Derivative Liability, Fair Value	(242.0)	(18.0)	(37.0)
Derivative Liability, Not Subject to Master Netting Arrangement	(7.0)	0.0	0.0
Derivative Netting Adjustments, Liabilities	0.0	0.0	0.0
Derivative Netting Adjustments, Assets	0.0	0.0	0.0
Derivative Asset, Subject to Master Netting Arrangement, after Offset	3.0	8.0	1.0
Derivative Liability, Subject to Master Netting Arrangement, after Offset	242.0	18.0	37.0
Forward sales contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	360.0	15.0	69.0
Derivative Liability, Fair Value	(6.0)	(18.0)	(4.0)
Derivative Asset, Not Subject to Master Netting Arrangement	20.0	1.0	2.0
Derivative Netting Adjustments, Liabilities	0.0	0.0	0.0
Derivative Netting Adjustments, Assets	0.0	0.0	0.0
Derivative Asset, Subject to Master Netting Arrangement, after Offset	360.0	15.0	69.0
Derivative Liability, Subject to Master Netting Arrangement, after Offset	6.0	18.0	4.0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	377,024.0	479,383.0	481,135.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	292.0	39.0	47.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	393.0	35.0	89.0
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	2,155.0	4.0	4.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	5.0	0.0	0.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	5.0	0.0	0.0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	146.0	180.0	118.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	1.0	1.0	0.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	2.0	0.0	2.0
Not Designated as Hedging Instrument [Member] | Interest Rate Lock Commitments
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	1,918.0	3,033.0	3,576.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	31.0	2.0	6.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	3.0	11.0	15.0
Not Designated as Hedging Instrument [Member] | Swaption
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	0.0	0.0	50.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0.0	0.0	0.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0.0	0.0	0.0
Not Designated as Hedging Instrument [Member] | Forward purchase contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	8,226.0	11,714.0	6,551.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	249.0	18.0	37.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	3.0	8.0	1.0
Not Designated as Hedging Instrument [Member] | Forward sales contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	11,792.0	17,358.0	13,984.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	6.0	18.0	4.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	380.0	16.0	71.0
Not Designated as Hedging Instrument [Member] | Futures purchase contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	172,333.0	218,054.0	224,325.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0.0	0.0	0.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0.0	0.0	0.0
Not Designated as Hedging Instrument [Member] | Futures sales contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	180,454.0	229,040.0	232,527.0
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	0.0	0.0	0.0
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0.0	0.0	0.0
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	22.0	14.0	7.0
Derivative Liability, Fair Value	0.0	(55.0)	(57.0)
Derivative, Notional Amount	483.0	1,383.0	1,547.0
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	483.0	1,383.0	1,547.0
Derivative Instruments in Hedges, Assets, at Fair Value	22.0	14.0	7.0
Fair Value Hedge Liabilities	$ 0.0	$ 55.0	$ 57.0