Basis Of Presentation And Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Basis Of Presentation And Significant Accounting Policies [Line Items]
Customer funds and cash and cash equivalents on deposit for regulatory requirements	$ 258	$ 173
Securities lending transactions, ratio of fair value of collateral on hold to fair value of securities on loan	102.00%	102.00%
Premiums receivable, allowance for doubtful accounts	$ 152	$ 142
Self-funded receivables, allowance for doubtful accounts	68	50
Other receivables, allowance for doubtful accounts	$ 744	648
Defined Benefit Plan, Alternative Method Used to Amortize Gain (Loss), Description	We determine the expected return on plan assets using the calculated value of plan assets, which recognizes changes in the fair value of plan assets in a systematic manner over three years. We apply a corridor approach to amortize unrecognized actuarial gains or losses. Under this approach, only accumulated net actuarial gains or losses in excess of 10% of the greater of the projected benefit obligation or the fair value of plan assets are amortized over the average remaining service or lifetime of the workforce as a component of net periodic benefit cost.
Employee stock purchase plan, purchase price per share as a percent of closing price	90.00%
Advertising and marketing expense	$ 511	588	$ 558
Patient Protection Affordable Care Act Health Insurance Provider Fee, annual amount to be collected by the Government through assessments to all health insurers subject to the fee		15,523
Patient Protection Affordable Care Act Health Insurance Provider Fee, amount paid		1,570
Retained Earnings (Accumulated Deficit)	29,724	27,088
Operating Lease, Impairment Loss	34	136	258
Long-term debt	23,849	22,756
Total shareholders' equity	36,307	36,060
Retained Earnings [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Total shareholders' equity	$ 29,724	27,088	$ 23,802	$ 22,538
Accounting Standards Update 2020-06 | Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Long-term debt		31
Deferred Tax and Other Liabilities, Noncurrent		(8)
Total shareholders' equity		$ (23)
Leasehold Improvements [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Depreciation Methods	Leasehold improvements are depreciated over the term of the related lease.
Minimum [Member] | Buildings and Improvements [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Minimum [Member] | Computer Equipment and Software [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Minimum [Member] | Internal-use software [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member] | Buildings and Improvements [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Maximum [Member] | Computer Equipment and Software [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Maximum [Member] | Furniture And Other Equipment [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Maximum [Member] | Internal-use software [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life	10 years