CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Gross billings	$ 4,314	$ 3,826	$ 13,040	$ 11,469
Worksite employee payroll costs	$ 3,611	$ 3,200	$ 10,828	$ 9,515