Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Depreciation and fixed asset basis differences, Assets	$ 0	$ 0
Allowances for professional liability and other risks, Assets	426	407
Accounts receivable, Assets	348	283
Compensation, Assets	502	487
Right-of-use lease obligations	428	416
Other, Assets	499	485
Deferred tax assets	2,203	2,078
Depreciation and fixed asset basis differences, Liabilities	737	678
Allowances for professional liability and other risks, Liabilities	0	0
Accounts receivable, Liabilities	0	0
Compensation, Liabilities	0	0
Right-of-use lease assets and obligations	419	409
Other, Liabilities	652	606
Deferred tax liabilities	$ 1,808	$ 1,693