Schedule IV Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reportable Segments
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 35,258	$ 38,579	$ 42,931
Ceded to Other Companies	8,342	8,350	8,360
Assumed from Other Companies	3,369	2,947	2,979
Net Amount	$ 30,285	$ 33,176	$ 37,550
Percent of Amount Assumed to Net	11.10%	8.90%	7.90%
Reportable Segments | General Insurance Companies
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 30,205	$ 33,970	$ 37,698
Ceded to Other Companies	7,533	7,561	7,604
Assumed from Other Companies	3,084	2,824	2,972
Net Amount	$ 25,756	$ 29,233	$ 33,066
Percent of Amount Assumed to Net	12.00%	9.70%	9.00%
Reportable Segments | Life and Retirement Companies
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 5,053	$ 4,609	$ 5,233
Ceded to Other Companies	809	789	756
Assumed from Other Companies	285	123	7
Net Amount	$ 4,529	$ 3,943	$ 4,484
Percent of Amount Assumed to Net	6.30%	3.10%	0.20%
Reportable Segments | Other
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 0	$ 0	$ 0
Ceded to Other Companies	0	0	0
Assumed from Other Companies	0	0	0
Net Amount	$ 0	$ 0	$ 0
Percent of Amount Assumed to Net	0.00%	0.00%	0.00%
Long-duration insurance in force
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 1,061,095	$ 1,025,653	$ 1,051,571
Ceded to Other Companies	202,402	174,363	177,025
Assumed from Other Companies	321	339	372
Net Amount	$ 859,014	$ 851,629	$ 874,918
Percent of Amount Assumed to Net	0.00%	0.00%	0.00%