CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDER'S EQUITY (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Premium on Common Stock	Retained Earnings
Balance at Dec. 31, 2015	$ 3,155.7	$ 100.9	$ 920.9	$ 2,133.9
Changes in Stockholders' Equity
Net income	238.3	0.0	0.0	238.3
Dividends declared on common stock	(125.0)	0.0	0.0	(125.0)
Stock-based compensation	1.7	0.0	1.7	0.0
Balance at Sep. 30, 2016	3,270.7	100.9	922.6	2,247.2
Balance at Dec. 31, 2016	3,252.1	100.9	923.2	2,228.0
Changes in Stockholders' Equity
Net income	263.9	0.0	0.0	263.9
Dividends declared on common stock	(105.0)	0.0	0.0	(105.0)
Stock-based compensation	1.9	0.0	1.9	0.0
Balance at Sep. 30, 2017	$ 3,412.9	$ 100.9	$ 925.1	$ 2,386.9