Difference between Federal Income Tax Rate and Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	21.00%	35.00%
Foreign tax credits	0.40%	(0.30%)	(6.40%)
Income subject to dividends-received deduction	(0.30%)	(18.30%)	(25.50%)
Tax-exempt interest	(1.00%)	(36.00%)	(94.10%)
State taxes, net of federal tax benefit	0.90%	13.80%	6.50%
Prior period adjustment	0.20%	(0.10%)	(3.30%)
Tax benefit from sale of subsidiary			(54.10%)
Other, net	(0.40%)	(18.10%)	(32.00%)
Effective tax rate	20.80%	(38.00%)	(173.90%)