Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders' Equity Note [Abstract]

Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax

	2018
(Millions of Dollars)	Gains and Losses on Cash Flow Hedges				Unrealized Gains and Losses on Marketable Securities			Defined Benefit Pension and Postretirement Items				Total
Accumulated other comprehensive (loss) income at Jan. 1	$	(20.9	)		$	0.1		$	(3.7	)		$	(24.5	)
Other comprehensive (loss) income before reclassifications (net of taxes of $0, $0 and $0.3, respectively)	—				(0.1		)	0.6				0.5
Losses reclassified from net accumulated other comprehensive loss:
Interest rate derivatives (net of taxes of $0.3, $0 and $0, respectively)	0.7			(a)	—			—				0.7
Amortization of net actuarial loss (net of taxes of $0, $0 and $0.1, respectively)	—				—			0.2			(b)	0.2
Net current period other comprehensive income (loss)	0.7				(0.1		)	0.8				1.4
Accumulated other comprehensive loss at Dec. 31	$	(20.2	)		$	—		$	(2.9	)		$	(23.1	)

	2019
(Millions of Dollars)	Gains and Losses on Cash Flow Hedges				Defined Benefit Pension and Postretirement Items				Total
Accumulated other comprehensive loss at Jan. 1	$	(20.2	)		$	(2.9	)		$	(23.1	)
Other comprehensive loss before reclassifications (net of taxes of $0 and $(0.1) respectively)	—				(0.4		)		(0.4		)
Losses reclassified from net accumulated other comprehensive loss:
Interest rate derivatives (net of taxes of $0.3 and $0, respectively) (a)	0.8			(a)	—				0.8
Amortization of net actuarial loss (net of taxes of $0 and $0.1, respectively)	—				0.2			(b)	0.2
Net current period other comprehensive income (loss)	0.8				(0.2		)		0.6
Accumulated other comprehensive loss at Dec. 31	$	(19.4	)		$	(3.1	)		$	(22.5	)