Fair Value Measurements (Details) - Changes in Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	$ 222	$ 242
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	3	9
Level 3 fair value category, total unrealized investment gains (losses) reported in increases in other comprehensive income (loss)	4	(4)
Level 3 fair value category purchases	44	149
Level 3 fair value category sales	(26)	(23)
Level 3 fair value category settlements/maturities	(19)	(71)
Gross transfers into Level 3	0	11
Gross transfers out of Level 3	(107)	(91)
Level 3 fair value category, ending balance	121	222
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	0	0
Fixed maturities [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	186	204
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	0	2
Level 3 fair value category, total unrealized investment gains (losses) reported in increases in other comprehensive income (loss)	4	(4)
Level 3 fair value category purchases	38	146
Level 3 fair value category sales	(1)	(11)
Level 3 fair value category settlements/maturities	(19)	(71)
Gross transfers into Level 3	0	11
Gross transfers out of Level 3	(107)	(91)
Level 3 fair value category, ending balance	101	186
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	0	0
Other investments [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance	36	38
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains	3	7
Level 3 fair value category, total unrealized investment gains (losses) reported in increases in other comprehensive income (loss)	0	0
Level 3 fair value category purchases	6	3
Level 3 fair value category sales	(25)	(12)
Level 3 fair value category settlements/maturities	0	0
Gross transfers into Level 3	0	0
Gross transfers out of Level 3	0	0
Level 3 fair value category, ending balance	20	36
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	$ 0	$ 0