Investments - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investment [Line Items]
Gross gains on fixed income securities	$ 168,000,000	$ 21,000,000	$ 409,000,000	$ 95,000,000
Gross loss on fixed income securities	(20,000,000)	(48,000,000)	(107,000,000)	(242,000,000)
Net unrealized gains related to changes in valuation of fixed income securities subsequent to impairment measurement date	179,000,000		179,000,000		$ 180,000,000
Limited partnership interests	7,990,000,000		7,990,000,000		7,505,000,000
Short-term investments	5,254,000,000		5,254,000,000		3,027,000,000
EMA limited partnerships
Investment [Line Items]
Limited partnership interests	6,230,000,000		6,230,000,000		5,730,000,000
Limited partnership interests
Investment [Line Items]
Limited partnership interests	1,760,000,000		1,760,000,000		$ 1,780,000,000
Mortgage loans, non-impaired
Investment [Line Items]
Allowance for credit losses, period increase (decrease)	0	0	0	0
Average impaired mortgage loans	$ 4,000,000	$ 4,000,000	$ 4,000,000	$ 4,000,000