Schedule II - Condensed Financial Information, Statements of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended															12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016	[1],[3]	Jun. 30, 2016	[1]	Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015	[1]	Jun. 30, 2015	[4]	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities
Shareholders' net income		$ 382	[1],[2]	$ 456		$ 510		$ 519	[1]	$ 426	[1]	$ 547		$ 588		$ 533	$ 1,867	$ 2,094	$ 2,102
Adjustments to reconcile shareholders' net income to net cash provided by (used in) operating activities:
Other liabilities																	124	423	202
Loss on extinguishment of debt																	0	100	0
Other, net	[5]																(10)	71	(30)
Net cash provided by (used in) operating activities	[5],[6]																4,026	2,933	2,158
Cash Flows from Investing Activities
Short term investments purchased																	(1,698)	(1,183)	(2,115)
Other, net																	(101)	0	(24)
Net cash provided by (used in) investing activities	[6]																(2,574)	(1,736)	(1,866)
Cash Flows from Financing Activities
Net change in short-term debt																	(148)	(21)	(112)
Net proceeds on issuance of long-term debt																	0	894	0
Repayment of long-term debt																	0	(938)	0
Issuance of common stock																	36	154	110
Repurchase of common stock																	(139)	(671)	(1,612)
Net cash provided by (used in) financing activities	[5]																(225)	(609)	(1,635)
Net increase (decrease) in cash and cash equivalents																	1,217	548	(1,375)
Cash and cash equivalents, January 1								1,968								1,420	1,968	1,420	2,795
Cash and cash equivalents, December 31		3,185								1,968							3,185	1,968	1,420
Parent Company [Member]
Cash Flows from Operating Activities
Shareholders' net income	[7]																1,867	2,094	2,102
Adjustments to reconcile shareholders' net income to net cash provided by (used in) operating activities:
Equity in income from subsidiaries																	(2,249)	(2,454)	(2,358)
Dividends received from subsidiaries																	580	880	1,648
Other liabilities																	(9)	112	(73)
Loss on extinguishment of debt																	0	100	0
Other, net	[8]																187	112	226
Net cash provided by (used in) operating activities	[8]																376	844	1,545
Cash Flows from Investing Activities
Short term investments purchased																	(3)	(54)	0
Other, net																	(8)	(14)	11
Net cash provided by (used in) investing activities																	(11)	(68)	11
Cash Flows from Financing Activities
Net change in amounts due to / from affiliates																	(78)	(161)	61
Net change in short-term debt																	(100)	0	0
Net proceeds on issuance of long-term debt																	0	894	0
Repayment of long-term debt																	0	(938)	0
Issuance of common stock																	36	154	110
Common dividends paid																	(10)	(10)	(11)
Repurchase of common stock																	(139)	(671)	(1,612)
Tax withholding on stock compensation	[8]																(72)	(79)	(53)
Net cash provided by (used in) financing activities	[8]																(363)	(811)	(1,505)
Net increase (decrease) in cash and cash equivalents																	2	(35)	51
Cash and cash equivalents, January 1								$ 16								$ 51	16	51	0
Cash and cash equivalents, December 31		$ 18								$ 16							$ 18	$ 16	$ 51

[1] Shareholders’ net income includes after-tax charges related to the Company’s proposed merger with Anthem as follows: $29 million in the third quarter of 2015, $28 million in the fourth quarter of 2015, $36 million in the first quarter of 2016, $26 million in the second quarter of 2016, $46 million in the third quarter of 2016 and $39 million in the fourth quarter of 2016. See Note 3 to the Consolidated Financial Statements for additional details.

[2] Shareholders’ net income includes an after-tax charge of $80 million for an allowance for the risk corridor receivable balance in the fourth quarter of 2016. See Note 22 to the Consolidated Financial Statements for additional details.

[3] Shareholders’ net income includes an after-tax charge of $25 million for charges related to litigation matters in the third quarter of 2016. See Note 21 to the Consolidated Financial Statements for a description of litigation matters.

[4] 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 5 to the Consolidated Financial Statements for additional details.

[5] As required in adopting Accounting Standard Update ("ASU") 2016-09, the Company retrospectively reclassified $79 million in 2015 and $53 million in 2014 of cash payments from operating to financing activities. These payments were related to employee tax obligations associated with stock compensation. The comparable amount reported in financing activities in 2016 was $72 million. See Note 2 for further discussion.

[6] As required in adopting ASU 2016-15, the Company retrospectively reclassified $137 million in 2015 and $111 million in 2014 of cash distributions of earnings from partnership investments from investing to operating activities. The comparable amount reported in operating activities in 2016 was $144 million. See Note 2 for further discussion.

[7] As required by the adoption of Accounting Standards Update 2016-09, the Company recorded $29 million of income tax benefits for the year ended December 31, 2016 that previously would have been reported in additional paid-in capital. No retrospective adjustments were made to income tax benefits for the years ended 2015 and 2014. See Note 1 for further discussion.

[8] As required in adopting ASU 2016-09, the Company retrospectively reclassified $79 million in 2015 and $53 million in 2014 of cash payments from operating to financing activities. These payments were related to employee tax obligations associated with stock compensation. The comparable amount reported in financing activities for the year ended December 31, 2016 was $72 million. See Note 1 for further discussion.