Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Valuation Allowance	$ 45	$ 95
Effective Income Tax Reconciliation Patient Protection Affordable Care Act Health Insurance Provider Fee	0	324	$ 0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	0	(28)	(1,108)
Reclassification of stranded tax effects resulting from the Tax Cuts and Jobs Act		91
Unrecognized tax benefits that would impact effective tax rate in future periods, if recognized	140	237
Unrecognized tax benefits that would impact additional paid-in capital in future periods, if recognized	2
Protective state income tax refund claims filed			310
Interest accrued	26	37
Net interest expense (benefit)	(11)	15	3
Unrecognized tax benefit change reasonably possible due to tax settlements - upper amount	(9)
Unrecognized tax benefit change reasonably possible due to tax settlements - lower amount	(102)
Federal tax net operating loss carry forwards	8
Income Taxes Paid	$ 1,403	738	1,503
Tax Cuts and Jobs Act [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount			$ (1,108)
Income tax expense (benefit) per diluted share			$ (4.14)
Health Insurance Provider fee [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Reconciliation Patient Protection Affordable Care Act Health Insurance Provider Fee		$ 324
Income tax expense (benefit) per diluted share		$ 1.23
Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2032