Investments - Other-than-temporary impairment losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	$ (46)	$ (120)	$ (144)
OTTI losses reclassified to (from) other comprehensive income	1	7	16
Net OTTI losses recognized in earnings	(45)	(113)	(128)
Municipal
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(1)	0	0
OTTI losses reclassified to (from) other comprehensive income	0	0	0
Net OTTI losses recognized in earnings	(1)	0	0
Corporate
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(7)	(23)	(25)
OTTI losses reclassified to (from) other comprehensive income	3	6	6
Net OTTI losses recognized in earnings	(4)	(17)	(19)
ABS
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(1)	(4)	(16)
OTTI losses reclassified to (from) other comprehensive income	(1)	0	10
Net OTTI losses recognized in earnings	(2)	(4)	(6)
RMBS
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	0	0	0
OTTI losses reclassified to (from) other comprehensive income	(2)	(1)	0
Net OTTI losses recognized in earnings	(2)	(1)	0
CMBS
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(9)	(15)	(1)
OTTI losses reclassified to (from) other comprehensive income	1	2	0
Net OTTI losses recognized in earnings	(8)	(13)	(1)
Fixed income securities
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(18)	(42)	(42)
OTTI losses reclassified to (from) other comprehensive income	1	7	16
Net OTTI losses recognized in earnings	(17)	(35)	(26)
Mortgage loans
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(1)	0	4
OTTI losses reclassified to (from) other comprehensive income	0	0	0
Net OTTI losses recognized in earnings	(1)	0	4
Equity securities
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(16)	(59)	(83)
OTTI losses reclassified to (from) other comprehensive income	0	0	0
Net OTTI losses recognized in earnings	(16)	(59)	(83)
Limited partnership interests
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(9)	(15)	(17)
OTTI losses reclassified to (from) other comprehensive income	0	0	0
Net OTTI losses recognized in earnings	(9)	(15)	(17)
Other
Other-than-temporary impairment losses by asset type
Total other-than-temporary impairment (“OTTI”) losses	(2)	(4)	(6)
OTTI losses reclassified to (from) other comprehensive income	0	0	0
Net OTTI losses recognized in earnings	$ (2)	$ (4)	$ (6)