Schedule I - Parent Company Financial Information (Condensed Statements of Comprehensive Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income	$ 145	$ 290	$ 344	$ 368	$ (30)	$ 368	$ 420	$ 473	$ 1,147	$ 1,231	$ 1,222
Other comprehensive income (loss):
Change in gross unrealized investment gains/losses									122	(338)	164
Effect of income taxes									(44)	124	(60)
Total change in unrealized investment gains/losses, net of tax									78	(214)	104
Reclassification adjustment for net realized gains included in investment income									(20)	(22)	(33)
Effect of income taxes									7	8	12
Total reclassification adjustment, net of tax									(13)	(14)	(21)
Other comprehensive (loss) income, net of tax									65	(228)	83
Comprehensive income									1,212	1,003	1,305
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income									$ 1,147	$ 1,231	$ 1,222