Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Depreciation and fixed asset basis differences, Assets	$ 0	$ 0
Allowances for professional liability and other risks, Assets	376	355
Accounts receivable, Assets	307	274
Compensation, Assets	292	256
Right-of-use lease obligations	369	0
Other, Assets	461	424
Deferred tax assets	1,805	1,309
Depreciation and fixed asset basis differences, Liabilities	601	340
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	366	0
Other, Liabilities	538	491
Deferred tax liabilities	$ 1,505	$ 831