Segment Information (Reconciliation of Amortization of DAC and VOBA, Net of Interest from Segments to Consolidated Net Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortization of DAC and VOBA, Net of Interest
Amortization of DAC and VOBA, net of interest	$ 976	$ 1,271	$ 1,283
Annuities Segment [Member]
Amortization of DAC and VOBA, Net of Interest
Amortization of DAC and VOBA, net of interest	401	383	342
Retirement Plan Services Segment [Member]
Amortization of DAC and VOBA, Net of Interest
Amortization of DAC and VOBA, net of interest	27	28	30
Life Insurance Segment [Member]
Amortization of DAC and VOBA, Net of Interest
Amortization of DAC and VOBA, net of interest	469	734	831
Group Protection Segment [Member]
Amortization of DAC and VOBA, Net of Interest
Amortization of DAC and VOBA, net of interest	$ 79	$ 126	$ 80