Fair Value Measurements - Information about Valuation Inputs for Fixed Income Securities Classified as Level 3 (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	$ 690	$ 595
Debt Securities, Available-for-sale	$ 2,265
Fair Value Inputs Yield Rate	11.60%
Asset-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Coupon rate	5.97%	5.97%
Fair Value Inputs Maturity	14 years 1 month 20 days	14 years 9 months 29 days
Yield	10.20%	10.50%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	$ 3,455	$ 3,354
Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	33	16
Hedge Funds, Multi-strategy [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	216	196
Interest Rate Contract [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	78	78
Illiquid Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other Investments	88	65
Corporate Obligations [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	3,320	3,215
Corporate Obligations [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	3,320	3,215
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	252	302
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Corporate Obligations [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	613	1,077
Fair Value, Recurring [Member] | Corporate Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	$ 12	0
Fair Value Inputs Maturity	2 years 9 months
Fair Value, Recurring [Member] | Corporate Obligations [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Debt Securities, Available-for-sale	$ 3,320	$ 3,215