Consolidated Statements of Shareholders' Comprehensive Income - USD ($) $ in Millions	3 Months Ended															12 Months Ended
	Dec. 31, 2016	[1],[2]	Sep. 30, 2016	[1],[3]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	[1]	Jun. 30, 2015	[4]	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Comprehensive Income [Abstract]
Shareholders' Net Income	$ 382		$ 456		$ 510		$ 519		$ 426		$ 547		$ 588		$ 533	$ 1,867	$ 2,094	$ 2,102
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities																(56)	(202)	143
Net unrealized appreciation (depreciation) on derivatives																(4)	15	11
Net translation of foreign currencies																(95)	(212)	(144)
Postretirement benefits liability adjustment																23	85	(426)
Shareholders' other comprehensive income (loss), net of tax																(132)	(314)	(416)
Shareholders' comprehensive income (loss)																$ 1,735	$ 1,780	$ 1,686

[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.