Schedule V - Valuation and Qualifying Accounts and Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commercial mortgage loans [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 5	$ 15	$ 12
Charged (Credited) to costs and expenses	1	0	7
Charged (Credited) to other accounts	0	0	0
Other deductions	(6)	(10)	(4)
Balance at end of period	0	5	15
Premiums, accounts and notes receivable [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	200	75	101
Charged (Credited) to costs and expenses	19	134	(10)
Charged (Credited) to other accounts	(11)	(8)	(15)
Other deductions	(1)	(1)	(1)
Balance at end of period	207	200	75
Deferred tax asset valuation allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	87	71	49
Charged (Credited) to costs and expenses	11	21	8
Charged (Credited) to other accounts	(26)	(5)	14
Other deductions	0	0	0
Balance at end of period	72	87	71
Reinsurance recoverables [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	3	3	4
Charged (Credited) to costs and expenses	0	0	0
Charged (Credited) to other accounts	0	0	(1)
Other deductions	0	0	0
Balance at end of period	$ 3	$ 3	$ 3