Consolidated Statements of Cash Flows (Parenthetical) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2017
Tax refund related to settlement agreement payment	$ 235,200,000
Payments of borrowings included in investing activities		$ 755,200,000
Total payment of borrowings		1,100,000,000
Value, shares repurchased		1,302,100,000
ASR Program
Stock repurchase program, authorized amount		400,000,000.0
Value, shares repurchased		$ 320,000,000