10-K Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017
Income Tax Contingency [Line Items]
Deferred Tax Liabilities, Net					$ 1,878	$ 2,712
Income tax expense	$ 354	$ 529	$ 1,554	$ 1,544	$ 1,712	$ 1,846	$ 1,666
Income tax expense (benefit) per diluted share					$ 7.05	$ 7.48	$ 6.55
Effective Income Tax Reconciliation Patient Protection Affordable Care Act Health Insurance Provider Fee					$ 0	$ 0	$ 330
Unrecognized tax benefits that would impact effective tax rate in future periods, if recognized					328	250
Unrecognized tax benefits that would impact additional paid-in capital in future periods, if recognized					2
Protective state income tax refund claims filed					92			$ 310
Net interest expense (benefit)					13	9	7
Interest accrued					55	42
Income Taxes Receivable	$ 258		$ 258		440	173
Income Taxes Paid					1,594	1,299	$ 1,790
Minimum [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefit change reasonably possible due to tax settlements - lower amount					33
Maximum [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefit change reasonably possible due to tax settlements - lower amount					143
Health Insurance Provider fee [Member]
Income Tax Contingency [Line Items]
Income tax expense (benefit) per diluted share							$ 1.30
Effective Income Tax Reconciliation Patient Protection Affordable Care Act Health Insurance Provider Fee							$ 330
Indefinite Carryforward Period | Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carry forwards					109
Limited Carryforward Period | Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carry forwards					$ 160
Earliest Tax Year [Member] | Federal [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date					Jan. 01, 2032
Earliest Tax Year [Member] | State [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date					Jan. 01, 2023
Latest Tax Year [Member] | Federal [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date					Dec. 31, 2042
Latest Tax Year [Member] | State [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date					Dec. 31, 2042
Other Noncurrent Assets [Member]
Income Tax Contingency [Line Items]
Deferred Tax Assets, Net					$ 137	103
Deferred tax liabilities, net [Member]
Income Tax Contingency [Line Items]
Deferred Tax Liabilities, Net					$ 2,015	$ 2,815