Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2018

Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]

Schedule of Net Benefit Costs

The following tables summarize the Company’s net periodic benefit cost for the three and nine months ended September 30, 2018 and 2017:

Puget Energy	Qualified Pension Benefits						SERP Pension Benefits				Other Benefits
	Three Months Ended September 30,
(Dollars in Thousands)	2018			2017			2018		2017		2018			2017
Components of net periodic benefit cost:
Service cost	$	6,218		$	5,020		$	212	$	228	$	17		$	18
Interest cost	6,917			7,093			530		571		113			125
Expected return on plan assets	(12,533		)	(11,945		)	—		—		(119		)	(115		)
Amortization of prior service cost	(495		)	(495		)	11		11		—			—
Amortization of net loss (gain)	716			—			394		269		(80		)	(101		)
Net periodic benefit cost	$	823		$	(327	)	$	1,147	$	1,079	$	(69	)	$	(73	)

Puget Energy	Qualified Pension Benefits						SERP Pension Benefits				Other Benefits
	Nine Months Ended September 30,
(Dollars in Thousands)	2018			2017			2018		2017		2018			2017
Components of net periodic benefit cost:
Service cost	$	17,068		$	15,060		$	635	$	685	$	52		$	54
Interest cost	20,477			21,279			1,590		1,714		333			375
Expected return on plan assets	(37,652		)	(35,837		)	—		—		(354		)	(346		)
Amortization of prior service cost	(1,485		)	(1,485		)	33		33		—			—
Amortization of net loss (gain)	1,640			—			1,185		807		(252		)	(302		)
Net periodic benefit cost	$	48		$	(983	)	$	3,443	$	3,239	$	(221	)	$	(219	)

Schedule of Changes in Projected Benefit Obligations

The following table summarizes the Company’s change in benefit obligation for the periods ended September 30, 2018 and December 31, 2017:

Puget Energy and Puget Sound Energy	Qualified Pension Benefits						SERP Pension Benefits						Other Benefits
	Nine Months Ended			Year Ended			Nine Months Ended			Year Ended			Nine Months Ended			Year Ended
(Dollars in Thousands)	September 30, 2018			December 31, 2017			September 30, 2018			December 31, 2017			September 30, 2018			December 31, 2017
Change in benefit obligation:
Benefit obligation at beginning of period	$	700,481		$	652,607		$	55,754		$	51,734		$	11,454		$	11,194
Service cost	17,068			20,081			635			913			52			72
Interest cost	20,477			28,373			1,590			2,285			333			500
Actuarial loss (gain)	3,991			40,945			—			2,722			82			725
Benefits paid	(33,183		)	(40,594		)	(1,561		)	(1,900		)	(816		)	(1,137		)
Medicare part D subsidy received	—			—			—			—			85			100
Administrative Expense	—			(931		)	—			—			—			—
Benefit obligation at end of period	$	708,834		$	700,481		$	56,418		$	55,754		$	11,190		$	11,454

Subsidiaries [Member]

Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]

Schedule of Net Benefit Costs

Puget Sound Energy	Qualified Pension Benefits						SERP Pension Benefits				Other Benefits
	Three Months Ended September 30,
(Dollars in Thousands)	2018			2017			2018		2017		2018			2017
Components of net periodic benefit cost:
Service cost	$	6,218		$	5,020		$	212	$	228	$	17		$	18
Interest cost	6,917			7,093			530		571		113			125
Expected return on plan assets	(12,542		)	(11,965		)	—		—		(119		)	(115		)
Amortization of prior service cost	(393		)	(393		)	11		11		—			—
Amortization of net loss (gain)	3,928			3,262			517		392		(134		)	(160		)
Net periodic benefit cost	$	4,128		$	3,017		$	1,270	$	1,202	$	(123	)	$	(132	)

Puget Sound Energy	Qualified Pension Benefits						SERP Pension Benefits				Other Benefits
	Nine Months Ended September 30,
(Dollars in Thousands)	2018			2017			2018		2017		2018			2017
Components of net periodic benefit cost:
Service cost	$	17,068		$	15,060		$	635	$	685	$	52		$	54
Interest cost	20,477			21,279			1,590		1,714		333			375
Expected return on plan assets	(37,680		)	(35,896		)	—		—		(354		)	(346		)
Amortization of prior service cost	(1,180		)	(1,180		)	33		33		—			—
Amortization of net loss (gain)	11,188			9,786			1,552		1,175		(417		)	(480		)
Net periodic benefit cost	$	9,873		$	9,049		$	3,810	$	3,607	$	(386	)	$	(397	)