Schedule IV (SUPPLEMENTAL INFORMATION CONCERNING REINSURANCE) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of Amount Assumed to Net									13.00%	21.00%	19.00%
Net Amount	$ 7,059	$ 7,688	$ 7,405	$ 6,597	$ 4,207	$ 4,719	$ 4,360	$ 3,927	$ 28,749	$ 17,213	$ 17,426
Assumed From Other Companies									3,744	3,676	3,336
Ceded To Other Companies									6,806	5,818	5,465
Direct Amount									$ 31,811	$ 19,355	$ 19,555
Property and Casualty [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of Amount Assumed to Net									14.00%	25.00%	23.00%
Net Amount									$ 23,796	$ 12,781	$ 12,767
Assumed From Other Companies									3,284	3,259	2,923
Ceded To Other Companies									6,407	5,373	4,940
Direct Amount									$ 26,919	$ 14,895	$ 14,784
Accident and Health [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of Amount Assumed to Net									6.00%	5.00%	4.00%
Net Amount									$ 3,951	$ 3,501	$ 3,678
Assumed From Other Companies									219	168	141
Ceded To Other Companies									315	351	434
Direct Amount									$ 4,047	$ 3,684	$ 3,971
Life [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Percentage of Amount Assumed to Net									24.00%	27.00%	28.00%
Net Amount									$ 1,002	$ 931	$ 981
Assumed From Other Companies									241	249	272
Ceded To Other Companies									84	94	91
Direct Amount									$ 845	$ 776	$ 800