Investments (excluding Consolidated Investment Entities) - OTTI OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Balance, beginning	$ 33	$ 46	$ 53
Additional credit impairments:
On securities not previously impaired	15	0	0
On securities previously impaired	1	2	4
Reductions:
Increase in cash flows	1	0	1
Securities sold, matured, prepaid or paid down	8	15	10
Balance, ending	$ 40	$ 33	$ 46