Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of New Accounting Pronouncements

Accounting Updates Adopted in 2016:

Accounting Standards Codification (ASC)	Description	Date of Adoption	Effect on Financial Statements
ASC 820 "Fair Value Measurement"	This update eliminated the requirement to categorize within the fair value hierarchy table investments whose fair value is measured at net asset value using the practical expedient. Instead, entities are required to disclose the fair value of these investments so that financial statement users can reconcile amounts reported in the fair value hierarchy table to the amounts reported on the consolidated balance sheets. The guidance is to be applied retrospectively.	January 1, 2016	The adoption of this update modified certain of our annual reporting period disclosures for invested assets held in our employee benefit plans but had no effect on our financial position or results of operations.
ASC 835 "Interest - Imputation of Interest"	This update simplified the presentation of deferred debt issuance costs by requiring these costs to be presented in the balance sheet as a reduction of the carrying amount of the debt liability to which the deferred costs relate, rather than classifying the deferred costs as an asset. This classification is consistent with the treatment of debt discounts. We applied the amendments in the update retrospectively, adjusting all prior periods in our consolidated financial statements and accompanying notes.	January 1, 2016	The adoption of this update resulted in the following reclassification adjustments to our consolidated balance sheets but had no effect on our financial position or results of operations.

	December 31, 2015
	Historical Accounting Method		As Adjusted		Effect of Change
	(in millions of dollars)
Consolidated Balance Sheets
Short-term Debt	$	352.4	$	352.0	$	(0.4	)
Long-term Debt	2,475.1		2,449.4		(25.7		)
Other Assets	663.5		637.4		(26.1		)

Accounting Updates Adopted in 2015:

ASC	Description	Date of Adoption	Effect on Financial Statements
ASC 860 "Transfers and Servicing"	This update changed the accounting for repurchase-to-maturity transactions and linked repurchase financings to secured borrowing accounting, which is consistent with the accounting for other repurchase agreements. The update also required disclosures for repurchase agreements, securities lending transactions, and repurchase-to-maturity transactions.	January 1, 2015, except for certain disclosures, which were effective April 1, 2015.	The adoption of this update expanded our disclosures, but had no effect on our financial position or results of operations.
ASC 323 "Investments - Equity Method and Joint Ventures"	This update permitted entities to make an accounting policy election to account for investments in qualified affordable housing projects using the proportional amortization method if certain conditions are met. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the income statement as a component of income tax expense (benefit). Additional disclosures concerning investments in qualified affordable housing projects were also required.	January 1, 2015	The adoption of this update resulted in the retrospective adjustment of all prior periods in our consolidated financial statements and accompanying notes.