Segment Information (Reconciliation of Net Investment Income From Segments to Consolidated) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Investment Income [Abstract]
Total net investment income	$ 4,844	$ 4,760	$ 4,631
Annuities Segment [Member]
Net Investment Income [Abstract]
Total net investment income	947	982	983
Retirement Plan Services Segment [Member]
Net Investment Income [Abstract]
Total net investment income	892	893	855
Life Insurance Segment [Member]
Net Investment Income [Abstract]
Total net investment income	2,546	2,496	2,403
Group Protection Segment [Member]
Net Investment Income [Abstract]
Total net investment income	259	167	176
Other Operations [Member]
Net Investment Income [Abstract]
Total net investment income	$ 200	$ 222	$ 214