Schedule IV - Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Life insurance in force, Gross	$ 761,946	$ 790,570	$ 799,341
Life insurance in force, Ceded	575,495	612,356	642,890
Life insurance in force, Assumed	296,751	318,443	340,241
Life insurance in force, Net	$ 483,202	$ 496,657	$ 496,692
Percentage of Assumed to Net, Life insurance in force	61.40%	64.10%	68.50%
Direct premiums	$ 2,606	$ 3,284	$ 2,975
Ceded Premiums	1,677	1,711	1,612
Assumed premiums	1,192	1,222	1,191
Net premiums	$ 2,121	$ 2,795	$ 2,554
Percentage Assumed to Net, Premiums	56.20%	43.70%	46.60%
Individual and group life insurance contracts
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct premiums	$ 1,280	$ 1,335	$ 1,351
Ceded Premiums	1,535	1,583	1,476
Assumed premiums	1,191	1,221	1,189
Net premiums	$ 936	$ 973	$ 1,064
Percentage Assumed to Net, Premiums	127.20%	125.50%	111.70%
Accident and health
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct premiums	$ 1,051	$ 1,056	$ 948
Ceded Premiums	142	128	136
Assumed premiums	1	1	2
Net premiums	$ 910	$ 929	$ 814
Percentage Assumed to Net, Premiums	0.10%	0.10%	0.20%
Annuity Contracts
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct premiums	$ 275	$ 893	$ 676
Ceded Premiums	0	0	0
Assumed premiums	0	0	0
Net premiums	$ 275	$ 893	$ 676
Percentage Assumed to Net, Premiums	0.00%	0.00%	0.00%