v3.20.4
Investments - Fair Value Measurement Inputs (Detail)
$ in Millions
Dec. 31, 2020
USD ($)
yr
Dec. 31, 2019
USD ($)
yr
Level 3 assets | $ $ 627,073 $ 539,568
Level 3 assets [Member]    
Level 3 assets | $ 26,305 23,068
Corporate debt securities [Member] | Level 3 assets [Member] | Investments [Member]    
Level 3 assets | $ $ 5,286 $ 3,465
Corporate debt securities [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.195 0.298
Corporate debt securities [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.045 0.055
Corporate debt securities [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.102 0.12
Corporate debt securities [Member] | Level 3 assets [Member] | Recovery rate [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.700 1.000
Corporate debt securities [Member] | Level 3 assets [Member] | Recovery rate [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.100 0.250
Corporate debt securities [Member] | Level 3 assets [Member] | Recovery rate [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.507 0.685
Corporate debt securities [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 7.7 5.9
Corporate debt securities [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 3.0 2.9
Corporate debt securities [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 4.2 5.0
Corporate debt securities [Member] | Level 3 assets [Member] | Multiples [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 29.3 24.4
Corporate debt securities [Member] | Level 3 assets [Member] | Multiples [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.6 0.6
Corporate debt securities [Member] | Level 3 assets [Member] | Multiples [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 6.9 7.0
Securities backed by real estate [Member] | Level 3 assets [Member] | Investments [Member]    
Level 3 assets | $ $ 998 $ 595
Securities backed by real estate [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.524 0.203
Securities backed by real estate [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.082 0.094
Securities backed by real estate [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.175 0.16
Securities backed by real estate [Member] | Level 3 assets [Member] | Recovery rate [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.578 0.344
Securities backed by real estate [Member] | Level 3 assets [Member] | Recovery rate [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.216 0.331
Securities backed by real estate [Member] | Level 3 assets [Member] | Recovery rate [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.337 0.335
Securities backed by real estate [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 3.6 3.0
Securities backed by real estate [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.4 0.4
Securities backed by real estate [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 2.7 0.9
Equity Securities [Member] | Level 3 assets [Member] | Investments [Member]    
Level 3 assets | $ $ 9,642 $ 10,903
Equity Securities [Member] | Level 3 assets [Member] | Multiples [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 27.9 36.0
Equity Securities [Member] | Level 3 assets [Member] | Multiples [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.6 0.8
Equity Securities [Member] | Level 3 assets [Member] | Multiples [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 9.0 8.0
Equity Securities [Member] | Level 3 assets [Member] | Discount rate/yield [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.385 0.203
Equity Securities [Member] | Level 3 assets [Member] | Discount rate/yield [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.040 0.021
Equity Securities [Member] | Level 3 assets [Member] | Discount rate/yield [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.135 0.134
Equity Securities [Member] | Level 3 assets [Member] | Capitalization rate [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.141 0.151
Equity Securities [Member] | Level 3 assets [Member] | Capitalization rate [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.037 0.036
Equity Securities [Member] | Level 3 assets [Member] | Capitalization rate [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.63 0.61
Other debt obligations [Member] | Level 3 assets [Member] | Investments [Member]    
Level 3 assets | $ $ 497 $ 319
Other debt obligations [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 0.062 0.052
Other debt obligations [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.017 0.034
Other debt obligations [Member] | Level 3 assets [Member] | Yield [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 0.035 0.045
Other debt obligations [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Maximum [Member]    
Investments measurement input 10.3 8.0
Other debt obligations [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Minimum [Member]    
Investments measurement input 0.2 4.0
Other debt obligations [Member] | Level 3 assets [Member] | Duration [Member] | Investments [Member] | Weighted Average [Member]    
Investments measurement input 6.4 6.7