Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Depreciation and fixed asset basis differences, Assets	$ 0	$ 0
Allowances for professional liability and other risks, Assets	495	443
Accounts receivable, Assets	351	363
Compensation, Assets	359	334
Other, Assets	794	845
Deferred tax assets	1,999	1,985
Depreciation and fixed asset basis differences, Liabilities	235	222
Allowances for professional liability and other risks, Liabilities	0	0
Accounts receivable, Liabilities	0	0
Compensation, Liabilities	0	0
Other, Liabilities	918	820
Deferred tax liabilities	$ 1,153	$ 1,042