CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Gross billings	$ 3,826	$ 3,362	$ 11,469	$ 10,231
Worksite employee payroll costs	$ 3,200	$ 2,802	$ 9,515	$ 8,469