Income Taxes - Differences Between Statutory Income Tax Rate and Effective Income Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (decrease) resulting from:
Tax at statutory rate	$ 39	$ 129	$ 383	$ 38
Tax-exempt income from municipal bonds	(5)	(5)	(15)	(15)
Dividend received exclusion	(5)	(5)	(14)	(13)
Other	2	11	(6)	6
Total provision for income taxes	$ 31	$ 130	$ 348	$ 16
Increase (decrease) resulting from:
Tax at statutory rate	21.00%	21.00%	21.00%	21.00%
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent	(2.70%)	(0.80%)	(0.80%)	(8.20%)
Effective Income Tax Rate Reconciliation, Deduction, Dividend, Percent	(2.70%)	(0.80%)	(0.80%)	(7.10%)
Other	1.20%	1.80%	(0.30%)	3.00%
Provision for income taxes	16.80%	21.20%	19.10%	8.70%