Investments (Allowance for Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning of year	$ 112	$ 119
Addition to (release of) allowance for losses	(6)	(7)
Charge-offs, net of recoveries	(1)	0
Change in foreign exchange	1	0
Total ending balance	106	112
Commercial Mortgage Loans
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning of year	97	104
Addition to (release of) allowance for losses	0	(7)
Charge-offs, net of recoveries	(1)	0
Change in foreign exchange	0	0
Total ending balance	96	97
Agricultural Property Loans
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning of year	2	1
Addition to (release of) allowance for losses	0	1
Charge-offs, net of recoveries	0	0
Change in foreign exchange	0	0
Total ending balance	2	2
Residential Property Loans
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning of year	3	5
Addition to (release of) allowance for losses	(1)	(2)
Charge-offs, net of recoveries	0	0
Change in foreign exchange	0	0
Total ending balance	2	3
Other Collateralized Loans
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning of year	0	0
Addition to (release of) allowance for losses	0	0
Charge-offs, net of recoveries	0	0
Change in foreign exchange	0	0
Total ending balance	0	0
Uncollateralized Loans
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for credit losses, beginning of year	10	9
Addition to (release of) allowance for losses	(5)	1
Charge-offs, net of recoveries	0	0
Change in foreign exchange	1	0
Total ending balance	$ 6	$ 10