Goodwill And Other Intangible Assets (Components Of Other Intangible Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Gross Carrying Amount, Finite Lived Intangibles	$ 4,096.3	$ 3,550.8
Accumulated Amortization, Finite Lived Intangibles	(3,018.2)	(2,876.2)
Net Carrying Amount, Finite Lived Intangibles	1,078.1	674.6
Gross Carrying Amount, Indefinite Lived Intangibles	7,290.3	7,290.3
Net Carrying Amount, Indefinite Lived Intangibles	7,290.3	7,290.3
Gross Carrying Amount, Total Intangible Assets	11,386.6	10,841.1
Accumulated Amortization, Total Intangible Assets	(3,018.2)	(2,876.2)
Net Carrying Amount, Total Intangible Assets	8,368.4	7,964.9
Blue Cross And Blue Shield And Other Trademarks [Member]
Intangible Assets [Line Items]
Gross Carrying Amount, Indefinite Lived Intangibles	6,298.7	6,298.7
Net Carrying Amount, Indefinite Lived Intangibles	6,298.7	6,298.7
State Medicaid Licenses [Member]
Intangible Assets [Line Items]
Gross Carrying Amount, Indefinite Lived Intangibles	991.6	991.6
Net Carrying Amount, Indefinite Lived Intangibles	991.6	991.6
Customer Relationships [Member]
Intangible Assets [Line Items]
Gross Carrying Amount, Finite Lived Intangibles	3,724.9	3,310.9
Accumulated Amortization, Finite Lived Intangibles	(2,877.8)	(2,759.7)
Net Carrying Amount, Finite Lived Intangibles	847.1	551.2
Provider And Hospital Relationships [Member]
Intangible Assets [Line Items]
Gross Carrying Amount, Finite Lived Intangibles	187.4	150.5
Accumulated Amortization, Finite Lived Intangibles	(73.2)	(65.9)
Net Carrying Amount, Finite Lived Intangibles	114.2	84.6
Other [Member]
Intangible Assets [Line Items]
Gross Carrying Amount, Finite Lived Intangibles	184.0	89.4
Accumulated Amortization, Finite Lived Intangibles	(67.2)	(50.6)
Net Carrying Amount, Finite Lived Intangibles	$ 116.8	$ 38.8