Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Remaining Contractual Maturities for Chattel Paper Agreements

As of December 31,2017, the remaining contractual maturities of the chattel paper agreements were as follows:

(In thousands)		2018		2019		2020		2021		2022		Thereafter
Repurchase-to-Maturity Transactions:
Loans	$	538	$	542	$	537	$	431	$	385	$	697

Straight-Line Depreciation Rates

Provisions at composite straight-line depreciation rates approximate the following percentages for the cost of depreciable property:

	2017	2016	2015
Electric(a)(b)	3.0 %	2.5 %	2.6 %
Gas(a)	2.1 %	2.1 %	1.7 %
Nonregulated	2.3 %	2.3 %	2.4 %

(a) In December 2015, the PSCW approved new depreciation rates, which were implemented and became effective as of January 1, 2016.

(b) In September 2016, the PSCW approved new depreciation rates for Columbia effective January 1, 2017.