Stockholders' Deficit - Cash Dividends Paid (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended					6 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Cash Dividends Paid
Common stock dividends (USD per share)		$ 0.225	$ 0.225	$ 0.20	$ 0.20
Cash dividends paid		$ 92.5	$ 92.4	$ 85.5	$ 87.4	$ 184.9	$ 172.9
Subsequent Event
Cash Dividends Paid
Common stock dividends (USD per share)	$ 0.225