Stockholders' Equity Dividends table (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Cash dividends per common share	$ 3.42	$ 3.34	$ 3.26
Cash dividends per preferred share	$ 0.03	$ 0.03	$ 0.03
Payment Of Special Cash Dividend	$ 37.0	$ 37.3	$ 37.4
Regular quarterly cash dividend
Class of Stock [Line Items]
Cash dividends per common share	$ 1.92	$ 1.84	$ 1.76
Special cash dividend
Class of Stock [Line Items]
Cash dividends per common share	$ 1.50	$ 1.50	$ 1.50