Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Dividends per share on common stock	$ 0.64	$ 0.61	$ 0.52
Settlement share transfer and excess tax benefit	$ 0.0	$ (2.9)	$ 46.2	[1]

[1] In 2015, we recorded an out-of-period adjustment of $46.2 million related to excess tax benefits from the Settlement agreement. Refer to Note 16, “Income Taxes” of the Notes to Consolidated Financial Statements for further details.