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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Increase (decrease) resulting from:
Tax at statutory rate	$ 62	$ 130	$ 355	$ 175
Tax-exempt income from municipal bonds	(5)	(5)	(14)	(15)
Dividend received exclusion	(3)	(3)	(11)	(11)
Tax accounting method changes, amount	0	(50)	0	(50)
Other	(8)	(7)	(10)	(6)
Total provision for income taxes	$ 46	$ 65	$ 320	$ 93
Increase (decrease) resulting from:
Tax at statutory rate	21.00%	21.00%	21.00%	21.00%
Tax-exempt income from municipal bonds	(1.70%)	(0.80%)	(0.80%)	(1.80%)
Dividend received exclusion	(1.00%)	(0.50%)	(0.70%)	(1.30%)
Tax accounting method changes, percent	0.00%	(8.10%)	0.00%	(6.00%)
Other	(2.70%)	(1.10%)	(0.60%)	(0.70%)
Provision for income taxes	15.60%	10.50%	18.90%	11.20%