Investments (excluding Consolidated Investment Entities) - OTTI (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 21	$ 34	$ 83
No. of Securities | security	61	92	101
Write-downs related to credit impairments	$ 19	$ 8	$ 8
Impairment, Intent-related	$ 2	$ 26	$ 75
No. of Securities, Intent-related | security	18	26	47
State, municipalities and political subdivisions
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 1	$ 0	$ 0
No. of Securities | security	3	2	0
U.S. corporate public securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 1	$ 8	$ 29
No. of Securities | security	3	3	24
Impairment, Intent-related	$ 1	$ 7	$ 29
No. of Securities, Intent-related | security	3	2	23
Foreign corporate public securities and foreign governments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 2	$ 17	$ 44
No. of Securities | security	3	4	12
Impairment, Intent-related	$ 0	$ 16	$ 43
No. of Securities, Intent-related | security	0	3	11
Foreign corporate private securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 15	$ 2	$ 1
No. of Securities | security	2	2	1
Residential mortgage-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 2	$ 7	$ 6
No. of Securities | security	47	80	59
Impairment, Intent-related	$ 1	$ 3	$ 2
No. of Securities, Intent-related | security	12	20	11
Other
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net other-than-temporary impairments recognized in earnings	$ 0	$ 0	$ 3
No. of Securities | security	3	1	5
Impairment, Intent-related	$ 0	$ 0	$ 1
No. of Securities, Intent-related | security	3	1	2