Schedule I - Condensed Financial Information of the Registrant - Condensed Balance Sheets (Parenthetical) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2021	Dec. 31, 2020
CONDENSED BALANCE SHEETS
Accumulated depreciation	$ 650.4	$ 659.9
Preferred stock, par value (USD per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Common stock, par value (USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common stock, shares issued	393,800,000	411,200,000
Common stock, shares outstanding	393,800,000	411,200,000
Parent Company | Reportable Legal Entities
CONDENSED BALANCE SHEETS
Accumulated depreciation	$ 50.1	$ 37.0
Preferred stock, par value (USD per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Common stock, par value (USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common stock, shares issued	393,800,000	411,200,000
Common stock, shares outstanding	393,800,000	411,200,000