Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Consolidated Balance Sheets [Abstract]
Allowance for doubtful patient accounts	$ 3,870	$ 3,773
Accumulated amortization	$ 883	$ 929
Preferred stock, par value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Common stock, par value per share	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	114,651,004	113,876,580
Common stock, shares outstanding	114,651,004	113,876,580