v3.21.2
Investments - Securities Accounted for As Available-for-Sale Included in Investments (Detail) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 44,851 $ 45,402
Fair Value $ 44,585 $ 46,016
Weighted Average Yield 0.51% 0.76%
U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 42,420 $ 43,310
Fair Value $ 42,241 $ 43,915
Weighted Average Yield 0.53% 0.78%
Non-U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 2,431 $ 2,092
Fair Value $ 2,344 $ 2,101
Weighted Average Yield 0.25% 0.21%
Less than 1 year [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 25 $ 25
Fair Value $ 25 $ 25
Weighted Average Yield 0.03% 0.08%
1 year to 5 years [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 37,056 $ 35,831
Fair Value $ 36,946 $ 36,158
Weighted Average Yield 0.47% 0.70%
5 years to 10 years [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 5,339 $ 7,454
Fair Value $ 5,270 $ 7,732
Weighted Average Yield 0.92% 1.19%
5 years to 10 years [Member] | Non-U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 2,431 $ 1,739
Fair Value $ 2,344 $ 1,744
Weighted Average Yield 0.25% 0.10%
Greater than 10 years [Member] | Non-U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost   $ 353
Fair Value   $ 357
Weighted Average Yield   0.74%