Schedule V (details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance recoverables [Member]
Schedule V [Roll Forward]
Valuation and qualifying accounts, balance at beginning of period	$ 116	$ 157	$ 203
Valuation and qualifying accounts, deductions	5	41	46
Valuation and qualifying accounts, balance at end of period	111	116	157
Allowance for uncollectible premiums receivable from underwriting activities [Member]
Schedule V [Roll Forward]
Valuation and qualifying accounts, balance at beginning of period	61	65	70
Valuation and qualifying accounts, charged to costs and expenses	38	35	38
Valuation and qualifying accounts, deductions	41	39	43
Valuation and qualifying accounts, balance at end of period	58	61	65
Allowance for uncollectible deductibles [Member]
Schedule V [Roll Forward]
Valuation and qualifying accounts, balance at beginning of period	34	35	36
Valuation and qualifying accounts, charged to costs and expenses	(2)	5	3
Valuation and qualifying accounts, deductions	6	6	4
Valuation and qualifying accounts, balance at end of period	$ 26	$ 34	$ 35