Reinsurance (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Funds held under reinsurance agreements, liability	$ 3,000	$ 3,200
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations	3,016	2,601	$ 1,379
Subsidiaries of Berkshire Hathaway Group [Member]
Largest Recoverables From Single Reinsurer	2,353
Gateway Rivers Insurance Company [Member]
Largest Recoverables From Single Reinsurer	350
Subsidiaries of Wilton Re[Member]
Largest Recoverables From Single Reinsurer	212
Significant Captive Program [Member]
Direct and ceded earned premiums	3,865	3,344	2,643
Reinsurance recoveries reported in insurance claims and policyholders' benefits reported on the Consolidated Statement of Operations	$ 2,621	$ 2,282	$ 1,458