Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		48 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2010
Catastrophe losses net of reinsurance	$ 36	$ 29
Loss Portfolio Transfer [Member]
Liability for Asbestos and Environmental Claims, Net					$ 1,600
Aggregate limit under AEP Loss Portfolio Transfer					4,000
Claim And Allocated Claim Adjustment Expense Reserves Under Existing Third Party Reinsurance Contracts					1,200
Reinsurance premium paid to NICO under AEP Loss Portfolio Transfer					2,000
Net reinsurance receivables transferrred to NICO under AEP Loss Portfolio Transfer					215
Total consideration paid to NICO under AEP Loss Portfolio Transfer					$ 2,200
Net AEP adverse development before consideration of LPT	200	0	$ 900
Asbestos adverse development	146
Environmental pollution adverse development	54
Retroactive reinsurance benefit recognized	(73)	(5)
Pretax impact of deferred retroactive reinsurance benefit	127	$ (5)
Cumulative amounts ceded under AEP Loss Portfolio Transfer	2,800			$ 2,600
Deferred reinsurance benefit yet to be recognized	368			241
Fair value of collateral trust account established by NICO under AEP Loss Portfolio Transfer	$ 2,700			$ 2,800