STATEMENTS OF CHANGES IN STOCKHOLDER'S EQUITY - USD ($) $ in Millions	Total	Common Stock	Premium on Common Stock	Retained Earnings
Balance at Dec. 31, 2013	$ 2,829.3	$ 100.9	$ 915.4	$ 1,813.0
Comprehensive income (loss)
Net income	292.0	0.0	0.0	292.0
Dividends declared on common stock	(120.0)	0.0	0.0	(120.0)
Stock-based compensation	2.9	0.0	2.9	0.0
Balance at Dec. 31, 2014	3,004.2	100.9	918.3	1,985.0
Comprehensive income (loss)
Net income	268.9	0.0	0.0	268.9
Dividends declared on common stock	(120.0)	0.0	0.0	(120.0)
Stock-based compensation	2.6	0.0	2.6	0.0
Balance at Dec. 31, 2015	3,155.7	100.9	920.9	2,133.9
Comprehensive income (loss)
Net income	284.1	0.0	0.0	284.1
Dividends declared on common stock	(190.0)	0.0	0.0	(190.0)
Stock-based compensation	2.3	0.0	2.3	0.0
Balance at Dec. 31, 2016	$ 3,252.1	$ 100.9	$ 923.2	$ 2,228.0