Investments - Held-to-Maturity Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 4,699	$ 5,301
Fair Value	$ 4,873	$ 5,637
Weighted Average Yield	2.13%	2.15%
U.S. government obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 4,054	$ 4,561
Fair Value	$ 4,200	$ 4,883
Weighted Average Yield	2.30%	2.33%
U.S. government obligations [Member] \| Less than 1 year [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		$ 501
Fair Value		$ 513
Weighted Average Yield		2.53%
U.S. government obligations [Member] \| 1 year to 5 years [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 4,054	$ 2,529
Fair Value	$ 4,200	$ 2,695
Weighted Average Yield	2.30%	2.34%
U.S. government obligations [Member] \| 5 years to 10 years [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		$ 1,531
Fair Value		$ 1,675
Weighted Average Yield		2.25%
Securities backed by real estate [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 645	$ 740
Fair Value	$ 673	$ 754
Weighted Average Yield	1.04%	1.08%
Securities backed by real estate [Member] \| 5 years to 10 years [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3	$ 4
Fair Value	$ 3	$ 3
Weighted Average Yield	2.78%	2.56%
Securities backed by real estate [Member] \| Greater than 10 years [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 642	$ 736
Fair Value	$ 670	$ 751
Weighted Average Yield	1.03%	1.08%