Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Health Care Reform Industry Assessment Fee Expense	$ 311	$ 238
Allowance for doubtful accounts and unrecoverable reinsurance	78	105
Amortization for policy acquisition costs recorded primarily in other operating expense	286	289	$ 255
Goodwill	$ 6,019	5,989	$ 6,029
Finite Lived Intangible Assets Amortization Method	accelerated or straight-line basis
Future policy benefits interest rate assumptions range low	0.10%
Future policy benefits interest rate assumptions range high	9.00%
Discount rate assumption for LTD and Workers' comp claim liabilities range low	4.40%
Discount rate assumption for LTD and Workers' comp claim liabilities range high	5.70%
Discounted liability for long-term disability and workers' compensation business	$ 3,700	$ 3,900
Business Acquisition [Line Items]
Percent of ASO fees reimbursed for performance guarantees	1.00%
Percent of Administrative Service Only fees at risk for performance guarantees	12.00%
Percent of total life insurance in force that is participating business	1.00%	1.00%	1.00%
Minimum [Member]
Finite Lived Intangible Assets Useful Life	5 years
Maximum [Member]
Finite Lived Intangible Assets Useful Life	30 years
Global Health Care [Member]
Goodwill	$ 5,700
Global Supplemental Benefits [Member]
Goodwill	300
Restatement Adjustment [Member] | Accounting Standards Update 2015-03 [Member] | Accumulated Other Comprehensive Income [Member] | Minimum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impact of new guidance on equity if adopted	(10)
Restatement Adjustment [Member] | Accounting Standards Update 2015-03 [Member] | Retained Earnings [Member] | Maximum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impact of new guidance on equity if adopted	$ 10
Building And Building Improvements Member | Minimum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	10 years
Building And Building Improvements Member | Maximum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	40 years
Internal-use software [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	1 year
Internal-use software [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	5 years
Internally developed software | Minimum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	3 years
Internally developed software | Maximum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	7 years
Furniture and equipment (including computer equipment) | Minimum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	3 years
Furniture and equipment (including computer equipment) | Maximum [Member]
Property Plant And Equipment [Line Items]
Property Plant And Equipment Useful Life	10 years