Commitments And Contingencies (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Commitments And Contingencies [Line Items]
Gross premium tax rate, state of California	2.35%
Merger Agreement, Termination Fee	$ 1,850
Minimum [Member]
Commitments And Contingencies [Line Items]
Estimate of possible loss on loss contingencies	0
Maximum [Member]
Commitments And Contingencies [Line Items]
Estimate of possible loss on loss contingencies	250
Anthem, Inc. v. Express Scripts, Inc. [Member]
Commitments And Contingencies [Line Items]
Proceeds originally received at time of divestiture	4,675
Anthem, Inc. v. Express Scripts, Inc. [Member] | Damages for Pharmacy Pricing [Member]
Commitments And Contingencies [Line Items]
Approximate amount of damages sought for breaches	14,800
Anthem, Inc. v. Express Scripts, Inc. [Member] | Damages for Operational Breaches [Member]
Commitments And Contingencies [Line Items]
Approximate amount of damages sought for breaches	158
Cyber Attack [Member]
Commitments And Contingencies [Line Items]
Settlement amount	$ 115