Fair Value Measurements - Debt at Carrying and Fair Value (Details) (Income Approach Valuation Technique, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
PUGET SOUND ENERGY, INC. | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	$ 3,763,259	$ 3,763,258
PUGET SOUND ENERGY, INC. | Carrying Amount | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated notes	250,000	250,000
Long-term Debt, Fixed Rate, Net of Discount, Fair Value Disclosure	3,513,259	3,513,258
PUGET SOUND ENERGY, INC. | Total
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	4,713,708	4,307,821
PUGET SOUND ENERGY, INC. | Total | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated notes	276,235	269,366
Long-term Debt, Fixed Rate, Net of Discount, Fair Value Disclosure	4,437,473	4,038,455
PUGET ENERGY | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	5,243,608	5,232,476
PUGET ENERGY | Carrying Amount | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated notes	250,000	250,000
Long-term Debt, Fixed Rate, Net of Discount, Fair Value Disclosure	4,694,608	4,683,476
Long-term Debt, Variable Rate, Net of Discount, Fair Value Disclosure	299,000	299,000
PUGET ENERGY | Total
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	6,658,789	6,162,680
PUGET ENERGY | Total | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated notes	276,235	269,366
Long-term Debt, Fixed Rate, Net of Discount, Fair Value Disclosure	6,083,554	5,594,314
Long-term Debt, Variable Rate, Net of Discount, Fair Value Disclosure	$ 299,000	$ 299,000