Summary of Significant Inputs Used by Third-Party Pricing Services for Certain Fair Value Measurements of Fixed Maturity Securities that Classified as Level 2 (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 63,544	$ 60,339
Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	5,602	5,025
Fixed maturity securities | State and Political Subdivisions
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,998	2,747
Fixed maturity securities | Non-U.S. government
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	1,542	1,350
Fixed maturity securities | U.S. corporate
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	34,395	32,111
Fixed maturity securities | Non-U.S. corporate
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	10,885	10,525
Fixed maturity securities | Residential mortgage-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,184	2,270
Fixed maturity securities | Commercial mortgage-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,970	3,026
Fixed maturity securities | Other asset-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,968	3,285
Level 2
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	59,289	56,148
Level 2 | Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	5,602	5,025
Level 2 | Fixed maturity securities | State and Political Subdivisions
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,935	2,645
Level 2 | Fixed maturity securities | Non-U.S. government
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	1,542	1,350
Level 2 | Fixed maturity securities | U.S. corporate
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	32,063	29,872
Level 2 | Fixed maturity securities | Non-U.S. corporate
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	9,191	8,840
Level 2 | Fixed maturity securities | Residential mortgage-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,160	2,243
Level 2 | Fixed maturity securities | Commercial mortgage-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,949	3,020
Level 2 | Fixed maturity securities | Other asset-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	2,847	$ 3,153
Level 2 | Third-Party Pricing Services | Fixed maturity securities | U.S. government, agencies and government-sponsored enterprises
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 5,602
Primary methodologies	Price quotes from trading desk, broker feeds
Significant inputs	Bid side prices, trade prices, Option Adjusted Spread (“OAS”) to swap curve, Bond Market Association OAS, Treasury Curve, Agency Bullet Curve, maturity to issuer spread
Level 2 | Third-Party Pricing Services | Fixed maturity securities | State and Political Subdivisions
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 2,935
Primary methodologies	Multi-dimensional attribute-based modeling systems, third-party pricing vendors
Significant inputs	Trade prices, material event notices, Municipal Market Data benchmark yields, broker quotes
Level 2 | Third-Party Pricing Services | Fixed maturity securities | Non-U.S. government
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 1,527
Primary methodologies	Matrix pricing, spread priced to benchmark curves, price quotes from market makers
Significant inputs	Benchmark yields, trade prices, broker quotes, comparative transactions, issuer spreads, bid-offer spread, market research publications, third-party pricing sources
Level 2 | Third-Party Pricing Services | Fixed maturity securities | U.S. corporate
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 30,874
Primary methodologies	Multi-dimensional attribute-based modeling systems, broker quotes, price quotes from market makers, OAS-based models
Significant inputs	Bid side prices to Treasury Curve, Issuer Curve, which includes sector, quality, duration, OAS percentage and change for spread matrix, trade prices, comparative transactions, Trade Reporting and Compliance Engine (“TRACE”) reports
Level 2 | Third-Party Pricing Services | Fixed maturity securities | Non-U.S. corporate
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 8,589
Primary methodologies	Multi-dimensional attribute-based modeling systems, OAS-based models, price quotes from market makers
Significant inputs	Benchmark yields, trade prices, broker quotes, comparative transactions, issuer spreads, bid-offer spread, market research publications, third-party pricing sources
Level 2 | Third-Party Pricing Services | Fixed maturity securities | Residential mortgage-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 2,160
Primary methodologies	OAS-based models, single factor binomial models, internally priced
Significant inputs	Prepayment and default assumptions, aggregation of bonds with similar characteristics, including collateral type, vintage, tranche type, weighted-average life, weighted-average loan age, issuer program and delinquency ratio, pay up and pay down factors, TRACE reports
Level 2 | Third-Party Pricing Services | Fixed maturity securities | Commercial mortgage-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 2,949
Primary methodologies	Multi-dimensional attribute-based modeling systems, pricing matrix, spread matrix priced to swap curves, Trepp commercial mortgage-backed securities analytics model
Significant inputs	Credit risk, interest rate risk, prepayment speeds, new issue data, collateral performance, origination year, tranche type, original credit ratings, weighted-average life, cash flows, spreads derived from broker quotes, bid side prices, spreads to daily updated swaps curves, TRACE reports
Level 2 | Third-Party Pricing Services | Fixed maturity securities | Other asset-backed
Fair value measurements Significant unobservable inputs [Line Items]
Available-for-sale debt securities	$ 2,847
Primary methodologies	Multi-dimensional attribute-based modeling systems, spread matrix priced to swap curves, price quotes from market makers
Significant inputs	Spreads to daily updated swaps curves, spreads derived from trade prices and broker quotes, bid side prices, new issue data, collateral performance, analysis of prepayment speeds, cash flows, collateral loss analytics, historical issue analysis, trade data from market makers, TRACE reports