Claim and Claim Adjustment Expense Reserves (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010
Catastrophe losses net of reinsurance	$ 156,000,000	$ 169,000,000	$ 391,000,000
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development Life & Group	(14,000,000)	(9,000,000)	(11,000,000)
Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development, Workers' Compensation Reinsurance Pool	(26,000,000)
Loss Portfolio Transfer [Member]
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO				1,600,000,000
Aggregate limit under A&EP Loss Portfolio Transfer				4,000,000,000
A&EP claim and allocated claim adjustment expense reserves ceded under existing third party reinsurance contracts transferred to NICO under A&EP Loss Portfolio Transfer				1,200,000,000
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer				2,000,000,000
Net reinsurance receivables transferrred to NICO under A&EP Loss Portfolio Transfer				215,000,000
Total consideration paid to NICO under AEP Loss Portfolio Transfer				2,200,000,000
Pretax impact of unrecognized deferred retroactive reinsurance benefit	(13,000,000)	189,000,000
Deferred reinsurance benefit yet to be recognized	176,000,000
Cumulative amounts ceded under AEP Loss Portfolio Transfer		2,500,000,000
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer	$ 3,400,000,000