Schedule II-Condensed Financial Information Of Registrant (Statement Of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income	$ 1,230.7	$ 746.9	$ 855.3	$ 1,009.9	$ 368.4	$ 617.8	$ 780.6	$ 703.0	$ 3,842.8	$ 2,469.8	$ 2,560.0
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized losses on financial instruments									(200.3)	(220.1)	(147.1)
Other-than-temporary impairment losses recognized in income									33.1	115.4	83.4
Loss (gain) on extinguishment of debt									282.4	0.0	(9.3)
Loss on disposal of assets									13.0	4.5	16.0
Deferred income taxes									(1,272.1)	126.9	(65.9)
Amortization, net of accretion									779.7	807.8	802.1
Depreciation expense									110.7	104.0	105.8
Share-based compensation									169.6	164.6	148.2
Excess tax benefits from share-based compensation									0.0	(53.5)	(95.8)
Changes in operating assets and liabilities:
Receivables, net									(22.2)	(1,380.5)	(42.9)
Other invested assets, current									(35.5)	(19.4)	5.9
Other assets									(629.0)	(127.7)	33.8
Accounts payable and accrued expenses									921.8	182.3	(123.4)
Other liabilities									(120.2)	605.7	686.4
Other, net									(164.6)	(96.5)	(5.1)
Net cash provided by operating activities									4,184.8	3,270.2	4,211.9
Investing activities
Changes in collateral and settlement of non-hedging derivatives									64.9	(34.5)	(36.5)
Changes in securities lending collateral									624.5	222.0	214.4
Other, net									11.9	(3.0)	(8.2)
Net cash (used in) provided by investing activities									(5,082.4)	(513.9)	(1,151.5)
Financing activities
Net proceeds from (repayments of) commercial paper borrowings									174.6	(53.2)	682.2
Proceeds from long-term borrowings									5,457.8	0.0	1,226.5
Repayments of long-term borrowings									(2,815.1)	0.0	(2,697.2)
Changes in securities lending payable									(624.5)	(222.0)	(214.4)
Changes in bank overdrafts									71.0	513.8	(243.8)
Premiums paid on equity call options									0.0	0.0	(16.7)
Proceeds from sale of put options									0.9	0.0	16.6
Repurchase and retirement of common stock									(1,997.7)	0.0	(1,515.8)
Change in collateral and settlements of debt-related derivatives									(149.0)	(360.4)	0.0
Cash dividends	(179.5)	$ (181.4)	$ (171.8)	(172.2)	(171.3)	$ (171.1)	$ (170.9)	(170.7)	(704.9)	(684.0)	(656.6)
Proceeds from issuance of common stock under employee stock plans									225.3	119.4	186.0
Taxes paid through withholding of common stock under employee stock plans									(46.5)	(65.7)	(95.9)
Excess tax benefits from share-based compensation									0.0	53.5	95.8
Net cash provided by (used in) financing activities									426.9	(798.6)	(3,093.3)
Change in cash and cash equivalents									(466.4)	1,961.8	(38.2)
Cash and cash equivalents at beginning of year				4,075.3				2,113.5	4,075.3	2,113.5	2,151.7
Cash and cash equivalents at end of year	3,608.9				4,075.3				3,608.9	4,075.3	2,113.5
Anthem, Inc. [Member]
Operating activities
Net income									3,842.8	2,469.8	2,560.0
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed earnings of subsidiaries									(2,436.7)	(502.4)	(287.8)
Net realized losses on financial instruments									18.2	195.0	3.8
Other-than-temporary impairment losses recognized in income									7.5	47.8	39.2
Loss (gain) on extinguishment of debt									282.4	0.0	(9.3)
Loss on disposal of assets									0.0	2.3	0.2
Deferred income taxes									(32.5)	(7.0)	55.0
Amortization, net of accretion									25.4	33.5	40.8
Depreciation expense									69.2	70.4	68.1
Share-based compensation									169.6	164.6	148.2
Excess tax benefits from share-based compensation									0.0	(53.5)	(95.8)
Changes in operating assets and liabilities:
Receivables, net									(17.1)	17.5	(17.9)
Other invested assets, current									(0.9)	1.3	(0.2)
Other assets									(102.0)	213.2	(106.9)
Amounts due from/to subsidiaries									(1,033.9)	(1,487.8)	420.5
Accounts payable and accrued expenses									490.5	43.9	103.4
Other liabilities									(61.0)	(30.7)	(231.4)
Income taxes									(6.4)	198.4	47.2
Other, net									(2.3)	5.1	(10.2)
Net cash provided by operating activities									1,212.8	1,381.4	2,726.9
Investing activities
Purchases of investments									(3,814.3)	(2,874.9)	(2,130.7)
Proceeds from sales, maturities, calls and redemptions of investments									2,594.7	3,309.8	3,076.6
Changes in collateral and settlement of non-hedging derivatives									64.9	(34.5)	(36.5)
Capitalization of subsidiaries									(124.2)	(295.0)	(939.7)
Changes in securities lending collateral									25.0	91.8	94.0
Purchases of property and equipment, net of sales									(44.0)	(98.7)	(51.1)
Other, net									18.7	(7.9)	1.5
Net cash (used in) provided by investing activities									(1,279.2)	90.6	14.1
Financing activities
Net proceeds from (repayments of) commercial paper borrowings									174.6	(53.2)	682.2
Proceeds from long-term borrowings									5,457.8	0.0	1,226.5
Repayments of long-term borrowings									(2,815.1)	0.0	(2,697.2)
Changes in securities lending payable									(25.2)	(90.9)	(94.2)
Changes in bank overdrafts									51.8	30.8	(89.3)
Premiums paid on equity call options									0.0	0.0	(16.7)
Proceeds from sale of put options									0.9	0.0	16.6
Repurchase and retirement of common stock									(1,997.7)	0.0	(1,515.8)
Change in collateral and settlements of debt-related derivatives									(149.0)	(360.4)	0.0
Cash dividends									(737.2)	(715.1)	(686.5)
Proceeds from issuance of common stock under employee stock plans									225.3	119.4	186.0
Taxes paid through withholding of common stock under employee stock plans									(46.5)	(65.7)	(95.9)
Excess tax benefits from share-based compensation									0.0	53.5	95.8
Net cash provided by (used in) financing activities									139.7	(1,081.6)	(2,988.5)
Change in cash and cash equivalents									73.3	390.4	(247.5)
Cash and cash equivalents at beginning of year				$ 882.7				$ 492.3	882.7	492.3	739.8
Cash and cash equivalents at end of year	$ 956.0				$ 882.7				$ 956.0	$ 882.7	$ 492.3