Investments - Other-than-temporary impairment losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	$ (3)	$ (4)	$ (5)	$ (45)
Included in OCI	(1)	(2)	(2)	2
Net OTTI losses recognized in earnings	(4)	(6)	(7)	(43)
Municipal
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	0	0	(1)
Included in OCI	0	0	0	0
Net OTTI losses recognized in earnings	0	0	0	(1)
Corporate
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses			0	(7)
Included in OCI			0	3
Net OTTI losses recognized in earnings			0	(4)
ABS
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	(1)	0	(1)
Included in OCI	(1)	0	(1)	0
Net OTTI losses recognized in earnings	(1)	(1)	(1)	(1)
RMBS
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	0	(1)	0
Included in OCI	0	0	0	(2)
Net OTTI losses recognized in earnings	0	0	(1)	(2)
CMBS
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	(3)	1	(3)	(8)
Included in OCI	0	(2)	(1)	1
Net OTTI losses recognized in earnings	(3)	(1)	(4)	(7)
Fixed income securities
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	(3)	0	(4)	(17)
Included in OCI	(1)	(2)	(2)	2
Net OTTI losses recognized in earnings	(4)	(2)	(6)	(15)
Mortgage loans
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	(1)	0	(1)
Included in OCI	0	0	0	0
Net OTTI losses recognized in earnings	0	(1)	0	(1)
Equity securities
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	(1)	0	(16)
Included in OCI	0	0	0	0
Net OTTI losses recognized in earnings	0	(1)	0	(16)
Limited partnership interests
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	(2)	0	(9)
Included in OCI	0	0	0	0
Net OTTI losses recognized in earnings	0	(2)	0	(9)
Other
OTTI losses
Total other-than-temporary impairment (“OTTI”) losses	0	0	(1)	(2)
Included in OCI	0	0	0	0
Net OTTI losses recognized in earnings	$ 0	$ 0	$ (1)	$ (2)