Fair Value Measurements (details) - Changes in Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	$ 268	$ 289
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	3	4
Level 3 fair value category, total unrealized investment gains (losses) reported in increases (decreases) in other comprehensive income	(3)	(1)
Level 3 fair value category purchases	203	233
Level 3 fair value category sales	(9)	(2)
Level 3 fair value category settlements/maturities	(41)	(90)
Gross transfers into Level 3	21	18
Gross transfers out of Level 3	(186)	(183)
Level 3 fair value category, ending balance	256	268
Level 3 fair value category, amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date	(1)
Fixed maturities [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	232	255
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	1	3
Level 3 fair value category, total unrealized investment gains (losses) reported in increases (decreases) in other comprehensive income	(4)	(2)
Level 3 fair value category purchases	202	232
Level 3 fair value category sales	(7)	(1)
Level 3 fair value category settlements/maturities	(41)	(90)
Gross transfers into Level 3	21	18
Gross transfers out of Level 3	(186)	(183)
Level 3 fair value category, ending balance	218	232
Other investments [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	36	34
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	2	1
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	1
Level 3 fair value category sales	(2)	(1)
Level 3 fair value category, ending balance	38	$ 36
Level 3 fair value category, amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date	$ (1)