Additional Information - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for reinsurance recoverables [Line Items]
Total rental expense	$ 70	$ 69	$ 67
Operating lease future minimum payments due in next year	65
Operating lease future minimum payments due in year two	57
Operating lease future minimum payments due in year three	50
Operating lease future minimum payments due in year four	40
Operating lease future minimum payments due in year five	35
Operating lease future minimum payments due after year five	79
Commitments to fund limited partnerships	949
Retirement and employee savings plan expense	37	45	43
Allowance for reinsurance recoverables
Allowance for reinsurance recoverables [Line Items]
Aggregate allowance for losses on reinsurance recoverables	18	20
Net expense reduction against the allowance for losses on reinsurance recoverables	(2)
Reinsurance recoverable write-offs	$ 2
Maximum | Allowance for reinsurance recoverables
Allowance for reinsurance recoverables [Line Items]
Net expense reduction against the allowance for losses on reinsurance recoverables		$ (1)	$ (1)