Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Purchase and retirement of common stock (in shares)		33,953,127
Purchase and retirement of common stock (in shares)	16,606,157	33,900,000	119,823,621
Dividends declared on common stock (in dollars per share)	$ 0.4	$ 0.4	$ 0.4
Issuance of shares of common stock pursuant to employee stock plans (in shares)	1,709,140	2,166,861	2,506,067