Segment Information (Reconciliation of Net Investment Income from Segments to Consolidated Net Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income [Abstract]
Total net investment income	$ 4,874	$ 4,827	$ 4,859
Parent Company [Member]
Net Investment Income [Abstract]
Total net investment income	3		1
Annuities Segment [Member]
Net Investment Income [Abstract]
Total net investment income	1,033	1,004	1,033
Retirement Plan Services Segment [Member]
Net Investment Income [Abstract]
Total net investment income	859	846	831
Life Insurance Segment [Member]
Net Investment Income [Abstract]
Total net investment income	2,562	2,541	2,529
Group Protection Segment [Member]
Net Investment Income [Abstract]
Total net investment income	176	184	180
Other Operations [Member]
Net Investment Income [Abstract]
Total net investment income	$ 244	$ 252	$ 286