Schedule V. Valuation and Qualifying Accounts (Schedule of valuation and qualifying accounts) (Details) - Allowance for doubtful accounts, insurance and reinsurance receivables - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in valuation allowances and reserves [Roll Forward]
Balance at beginning of period	$ 83	$ 89	$ 109
Charged to Costs and Expenses	(1)	(2)	(12)
Charged to other accounts	0	(1)	0
Deductions	(9)	(3)	(8)
Balance at end of period	$ 73	$ 83	$ 89