Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		48 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2010
Catastrophe losses net of reinsurance	$ 60	$ 56	$ 89	$ 130
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	(5)	24	(12)	49
Specialty [Member]
Favorable development in other professional liability and management liability related to lower than expected severity for professional services primarily in accident years 2010 and prior	38		41
Unfavorable development in other professional services related to increased claim frequency on public company management liability in accident years 2012 through 2014	37		37
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	(13)	(41)	(11)	(44)
Commercial [Member]
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	16	90	11	108
Loss Portfolio Transfer [Member]
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO							$ 1,600
Aggregate limit under AEP Loss Portfolio Transfer							4,000
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
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer							2,000
Net reinsurance receivables transferrred to NICO under A&EP Loss Portfolio Transfer							215
Total consideration paid to NICO under A&EP Loss Portfolio Transfer							$ 2,200
Net AEP adverse development before consideration of LPT	150	$ 0	150	$ 0	$ 900
Cumulative amounts ceded under A&EP Loss Portfolio Transfer	2,600		2,600			$ 2,500
Deferred reinsurance benefit yet to be recognized	255		255			176
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer	$ 3,100		$ 3,100			$ 3,400