Income Taxes - Differences Between 35 Percent Statutory Income Tax Rate and Effective Income Tax Rate (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 42	$ 76
Increase (decrease) resulting from:
Tax-exempt income from municipal bonds	(8)	(8)
Dividend received exclusion	(7)	(6)
Other	1	1
Total provision for income taxes	$ 28	$ 63
Tax at statutory rate	35.00%	35.00%
Increase (decrease) resulting from:
Tax-exempt income from municipal bonds	(6.70%)	(3.70%)
Dividend received exclusion	(5.90%)	(2.60%)
Other	1.10%	0.30%
Provision for income taxes	23.50%	29.00%