Medical Claims Payable (Reconciliation Of The Claims Development To The Claims Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 223,482
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	214,868
Net medical claims payable, end of year	8,614
Ceded medical claims payable, end of year	33	$ 34	$ 105	$ 539
Insurance lines other than short duration	195
Total gross medical claims payable, end of year	8,842	7,454
Commercial and Specialty Business Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	81,121
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	78,096
Net medical claims payable, end of year	3,025
Ceded medical claims payable, end of year	14	10	78	521
Total gross medical claims payable, end of year	3,039
Government Business Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	142,361
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	136,772
Net medical claims payable, end of year	5,589
Ceded medical claims payable, end of year	19	$ 24	$ 27	$ 18
Insurance lines other than short duration	195
Total gross medical claims payable, end of year	$ 5,803