10-K Medical Claims Payable (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Claims and Claims Adjustment Expense [Abstract]
Prior Year Claims and Claims Adjustment Expense	$ (1,342)	$ (901)	$ (869)	$ (1,703)	$ (637)
Short-Duration Insurance Contracts, Accident Year 2017 | Commercial and Specialty Business Segment [Member]
Medical Claims Payable [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net			$ 195
Short-Duration Insurance Contract, Cumulative Number of Reported Claims			360
Short-duration Insurance Contracts, Accident Year 2019 and Prior Member] | Commercial and Specialty Business Segment [Member]
Medical Claims Payable [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net				$ 597
Short-Duration Insurance Contract, Cumulative Number of Reported Claims				440
Short-Duration Insurance Contract, Accident Year 2019 [Member] | Commercial and Specialty Business Segment [Member]
Medical Claims Payable [Line Items]
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net					$ 14,550
Short-Duration Insurance Contract, Cumulative Number of Reported Claims					404