Fair Value Measurements (details) - Changes in Level 3 (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	$ 289	$ 284
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	2	16
Level 3 fair value category, total unrealized investment gains (losses) reported in increases (decreases) in other comprehensive income	(1)	(1)
Level 3 fair value category purchases	85	180
Level 3 fair value category sales		(58)
Level 3 fair value category settlements/maturities	(29)	(83)
Gross transfers into Level 3		15
Gross transfers out of Level 3	(42)	(64)
Level 3 fair value category, ending balance	304	289
Fixed maturities [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	255	230
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	1	4
Level 3 fair value category, total unrealized investment gains (losses) reported in increases (decreases) in other comprehensive income	(2)	(2)
Level 3 fair value category purchases	84	180
Level 3 fair value category sales		(25)
Level 3 fair value category settlements/maturities	(29)	(83)
Gross transfers into Level 3		15
Gross transfers out of Level 3	(42)	(64)
Level 3 fair value category, ending balance	267	255
Other investments [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	34	54
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	1	12
Level 3 fair value category, total unrealized investment gains (losses) reported in increases (decreases) in other comprehensive income	1	1
Level 3 fair value category purchases	1
Level 3 fair value category sales		(33)
Level 3 fair value category, ending balance	$ 37	$ 34