Short-Term Borrowings and Credit Arrangements (Tables)

12 Months Ended

Dec. 31, 2016

Line of Credit Facility [Line Items]

Schedule of Line of Credit Facilities [Table Text Block]

On December 12, 2016, we amended and restated our existing revolving credit facility to, among other things, increase the size of the facility to $400 million (from $350 million) and extend the maturity date to December 12, 2021 (from November 5, 2018). We retained an accordion feature that allows us to increase the size up to $450 million with the consent of the lenders. The facility does not amortize and is unsecured. The facility bears interest at the lower of prime or available rates tied to the Eurodollar rate plus a credit spread, ranging from 0.875% to 1.75%. A total of eight banks participate in the facility, with no one bank providing more than 16% of the total availability. There were no direct borrowings or letters of credit outstanding as of December 31, 2016. Commitment fees for the unsecured revolving line of credit were $0.4 million for each of the years ended December 31, 2016 and 2015.

The credit facility includes covenants that require us to meet certain financial tests, including a maximum debt to capitalization ratio not to exceed 65%. The facility also contains covenants which, among other things, limit our ability to engage in any consolidation or merger or otherwise liquidate or dissolve, dispose of property, and enter into transactions with affiliates. A default on the South Dakota or Montana First Mortgage Bonds would trigger a cross default on the credit facility; however a default on the credit facility would not trigger a default on any other obligations

Schedule of Short-term Debt

Short-term borrowings and the corresponding weighted average interest rates as of December 31 were as follows (dollars in millions):

	2016				2015
Short-Term Debt	Balance		Interest Rate		Balance		Interest Rate
Commercial Paper	$	300.8	1.07	%	$	229.9	0.82	%

The following information relates to commercial paper for the years ended December 31 (dollars in millions):

	2016			2015
Maximum short-term debt outstanding	$	300.8		$	267.8
Average short-term debt outstanding	$	210.7		$	192.8
Weighted-average interest rate	0.86		%	0.61		%