Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss on reinsurance transaction		$ 34
Anticipated amounts due from insureds related to losses under deductible policies	$ 1,200	$ 1,400
Structured Settlement Annuities, Interest Rate, Low End	5.50%	5.50%
Maximum interest rate used in determining present value of obligations of structured settlements not funded by annuities	8.00%	8.00%
Discounted reserves for unfunded structured settlements	$ 560	$ 582
Discounted reserves for unfunded structure settlements, discount amount	$ 880	$ 924
Minimum interest rate used to discount workers' compensation lifetime claim reserves and accident and health claim reserves	3.50%	3.50%
Maximum interest rate used to discount workers' compensation lifetime claim reserves and accident and health claim reserves	6.80%	6.80%
Discounted reserves for worker's compensation lifetime claim reserves and accident and health claim reserves	$ 2,600	$ 2,500
Discounted reserves for worker's compensation lifetime claim reserves and accident and health claim reserves, discount amount	653	$ 654
Long term care premium deficiency	296
Write off of deferred acquisition cost asset due to long term care premium deficiency	289
Adjustment to Active life reserves due to premium deficiency	$ 7
Minimum interest rate used to calculate reserves for long term care products	6.60%	4.50%
Maximum interest rate used to calculate reserves for payout annuity contracts	7.00%	7.90%
Liability balance for guaranty fund	$ 129	$ 131
Percentage of billed receivables compared to total reinsurance receivables	4% or less
Deposit assets	$ 3	3
Deposit liabilities	8	9
Investments in life settlement contracts	74	82
Increase (decrease) in fair value recognized on life settlement contracts	1	8	$ (2)
Gain recognized on matured life settlement contracts	24	25	15
Decreased Net Investment Income and amortized cost of fixed maturity securities due to a change in estimate effected by a change in accounting principle	$ 39
Decrease of Basic and Diluted Earnings per Share due to change in estimate effected by a change in accounting principle	$ 0.09
Decrease in shadow adjustment, net of tax	$ 177
Increase in shadow adjustment, net of tax		756
Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments	1,111	1,288
Foreign currency transaction gain (loss), before tax	$ (11)	$ (25)	$ 2
Weighted average number diluted shares outstanding adjustment	534	675	552
Antidilutive securities excluded from computation of earnings per share, amount	106	170	111
Interest paid, net	$ 152	$ 179	$ 164
Income taxes paid	$ 310	$ 313	$ 129
Furniture and Fixtures [Member]
Property, Plant and Equipment, Useful Life	7 years
Office Equipment [Member]
Property, Plant and Equipment, Useful Life	5 years
Building and Building Improvements [Member]
Property, Plant and Equipment, Useful Life	50 years
Minimum [Member]
Requisite service period for stock- based compensation expense	3 years
Minimum [Member] | Software [Member]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member]
Requisite service period for stock- based compensation expense	4 years
Maximum [Member] | Software [Member]
Property, Plant and Equipment, Useful Life	10 years