Segment Information - Reconciliation to Adjusted Income From Operations (Details) - USD ($) $ in Millions	3 Months Ended											12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Shareholders' Net Income	$ 426	[1]	$ 547	[1]	$ 588	[2]	$ 533	$ 467	$ 534	$ 573	$ 528	$ 2,094		$ 2,102	$ 1,476
After-tax adjustments to reconcile to adjusted income from operations:
Realized investment (gains) losses												(40)		(106)	(141)
Amortization of other acquired intangible assets												80	[3]	119	144
Results of GMIB business															(25)
Special items:
Debt extinguishment costs					$ 65							65
Merger-related transaction costs	$ 28		$ 29									57
Costs associated with a pharmacy benefit management ("PBM") services agreement															24
Charge related to reinsurance transaction															507
Charge for disability claims regulatory matter															51
Charge for organizational efficiency plan															40
Adjusted income from operations												2,256		2,115	2,076
Benefit of a 2015 acquisition in which the fair value of acquired net assets exceeded the purchase price												23
Operating Segments [Member] | Global Health Benefits Segment [Member]
Segment Reporting Information [Line Items]
Shareholders' Net Income												1,794		1,700	1,590
After-tax adjustments to reconcile to adjusted income from operations:
Realized investment (gains) losses												(30)		(54)	(73)
Amortization of other acquired intangible assets												84		106	127
Results of GMIB business															0
Special items:
Debt extinguishment costs												0
Merger-related transaction costs												0
Costs associated with a pharmacy benefit management ("PBM") services agreement															24
Charge related to reinsurance transaction															0
Charge for disability claims regulatory matter															0
Charge for organizational efficiency plan															31
Adjusted income from operations												1,848		1,752	1,699
Operating Segments [Member] | Global Supplemental Benefits Segment [Member]
Segment Reporting Information [Line Items]
Shareholders' Net Income												267		233	180
After-tax adjustments to reconcile to adjusted income from operations:
Realized investment (gains) losses												(1)		(3)	(5)
Amortization of other acquired intangible assets												(4)	[3]	13	17
Results of GMIB business															0
Special items:
Debt extinguishment costs												0
Merger-related transaction costs												0
Costs associated with a pharmacy benefit management ("PBM") services agreement															0
Charge related to reinsurance transaction															0
Charge for disability claims regulatory matter															0
Charge for organizational efficiency plan															8
Adjusted income from operations												262		243	200
Benefit of a 2015 acquisition in which the fair value of acquired net assets exceeded the purchase price												23
Operating Segments [Member] | Group Disability And Life Segment [Member]
Segment Reporting Information [Line Items]
Shareholders' Net Income												328		331	299
After-tax adjustments to reconcile to adjusted income from operations:
Realized investment (gains) losses												(4)		(14)	(40)
Amortization of other acquired intangible assets												0		0	0
Results of GMIB business															0
Special items:
Debt extinguishment costs												0
Merger-related transaction costs												0
Costs associated with a pharmacy benefit management ("PBM") services agreement															0
Charge related to reinsurance transaction															0
Charge for disability claims regulatory matter															51
Charge for organizational efficiency plan															1
Adjusted income from operations												324		317	311
Operating Segments [Member] | Other Operations Segment [Member]
Segment Reporting Information [Line Items]
Shareholders' Net Income												80		79	(371)
After-tax adjustments to reconcile to adjusted income from operations:
Realized investment (gains) losses												(5)		(11)	(23)
Amortization of other acquired intangible assets												0		0	0
Results of GMIB business															(25)
Special items:
Debt extinguishment costs												0
Merger-related transaction costs												0
Costs associated with a pharmacy benefit management ("PBM") services agreement															0
Charge related to reinsurance transaction															507
Charge for disability claims regulatory matter															0
Charge for organizational efficiency plan															0
Adjusted income from operations												75		68	88
Corporate [Member]
Segment Reporting Information [Line Items]
Shareholders' Net Income												(375)		(241)	(222)
After-tax adjustments to reconcile to adjusted income from operations:
Realized investment (gains) losses												0		(24)	0
Amortization of other acquired intangible assets												0		0	0
Results of GMIB business															0
Special items:
Debt extinguishment costs												65
Merger-related transaction costs												57
Costs associated with a pharmacy benefit management ("PBM") services agreement															0
Charge related to reinsurance transaction															0
Charge for disability claims regulatory matter															0
Charge for organizational efficiency plan															0
Adjusted income from operations												$ (253)		$ (265)	$ (222)

[1] Shareholders’ net income includes after-tax charges of $29 million in the third quarter of 2015 and $28 million in the fourth quarter of 2015 for advisory, legal and other transactions costs directly related to the Company’s proposed merger with Anthem. See Note 3 to the Consolidated Financial Statements for additional details.

[2] Shareholders’ net income includes an after-tax charge of $65 million for the early extinguishment of debt in the second quarter of 2015. See Note 15 to the Consolidated Financial Statements for additional details.

[3] As disclosed in Note 8, includes a one-time $23 million benefit.