Investments - Net Investment Income and Investment Gains (Losses) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Investment Income [Line Items]
Total investment income	$ 611	$ 549	$ 1,201	$ 1,160
Investment expenses	(14)	(14)	(27)	(26)
Net investment income	597	535	1,174	1,134
Investment gains (losses)	(14)	(14)	28	5
Fixed Maturity Securities [Member]
Net Investment Income [Line Items]
Total investment income	451	454	903	911
Investment gains (losses)	(19)	(7)	19	20
Short Term Investments [Member]
Net Investment Income [Line Items]
Total investment income	1	1	2	3
Investment gains (losses)	4		3	3
Limited Partnership Investments [Member]
Net Investment Income [Line Items]
Total investment income	116	84	203	230
Equity Securities [Member]
Net Investment Income [Line Items]
Total investment income	3	3	5	6
Investment gains (losses)		(2)	5	(15)
Income (Loss) from Trading Portfolio [Member]
Net Investment Income [Line Items]
Total investment income	30	1	70	(2)
Other [Member]
Net Investment Income [Line Items]
Total investment income	10	6	18	12
Derivative Instruments [Member]
Net Investment Income [Line Items]
Investment gains (losses)	$ 1	$ (5)	$ 1	$ (3)