Commitments And Contingencies (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2017	Sep. 30, 2017
Commitments And Contingencies [Line Items]
Gross premium tax rate, state of California		2.35%
Agreed upon settlement, amount, cyber attack incident		$ 115.0
Merger Agreement, Termination Fee		1,850.0
Anthem, Inc. v. Express Scripts, Inc. [Member]
Commitments And Contingencies [Line Items]
Excess pricing assertion, remaining term of the agreement at lawsuit filing date		13,000.0
Excess pricing assertion, post-termination transition period		1,800.0
Approximate amount of damages sought for operational breaches		158.0
Proceeds originally received at time of divestiture		4,675.0
Penn Treaty [Member]
Commitments And Contingencies [Line Items]
Estimated liability for guaranty association assessments	$ 253.8
Minimum [Member]
Commitments And Contingencies [Line Items]
Estimate of possible loss on loss contingencies		0.0
Maximum [Member]
Commitments And Contingencies [Line Items]
Estimate of possible loss on loss contingencies		$ 250.0