Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Income tax expense	$ 1,666	$ 1,178	$ 1,318
Effective Income Tax Reconciliation Patient Protection Affordable Care Act Health Insurance Provider Fee	$ 330	$ 0	324
Income tax expense (benefit) per diluted share	$ 6.55	$ 4.53
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	$ 227	140
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	33	26
Net interest expense (benefit)	7	(11)	15
Unrecognized tax benefit change reasonably possible due to tax settlements - upper amount	(147)
Unrecognized tax benefit change reasonably possible due to tax settlements - lower amount	(15)
Income Taxes Paid	1,790	$ 1,403	738
Health Insurance Provider fee [Member]
Income Tax Contingency [Line Items]
Effective Income Tax Reconciliation Patient Protection Affordable Care Act Health Insurance Provider Fee	$ 330		$ 324
Income tax expense (benefit) per diluted share	$ 1.30		$ 1.23
Latest Tax Year [Member] | Federal [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Latest Tax Year [Member] | State [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2040
Earliest Tax Year [Member] | Federal [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2033
Earliest Tax Year [Member] | State [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2022
Indefinite Carryforward Period | Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carry forwards	$ 7
Limited Carryforward Period | Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carry forwards	$ 40