Retirement Plans and Other Benefits (Tables)

6 Months Ended

Jun. 30, 2015

Compensation and Retirement Disclosure [Abstract]

Schedule of net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction, billed to electric plant participants or charged or amortized to the regulatory asset)

The following table provides details of the plans’ net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction, billed to electric plant participants or charged or amortized to the regulatory asset) (dollars in millions):

	Pension Benefits												Other Benefits
	Three Months Ended   June 30,						Six Months Ended   June 30,						Three Months Ended   June 30,						Six Months Ended   June 30,
	2015			2014			2015			2014			2015			2014			2015			2014
Service cost — benefits earned during the period	$	14		$	12		$	30		$	27		$	4		$	5		$	8		$	9
Interest cost on benefit obligation	31			33			62			65			7			11			14			23
Expected return on plan assets	(45		)	(39		)	(90		)	(79		)	(9		)	(13		)	(18		)	(25		)
Amortization of:
Prior service cost	—			—			—			—			(9		)	—			(19		)	—
Net actuarial loss	8			3			16			5			—			—			2			—
Net periodic benefit cost	$	8		$	9		$	18		$	18		$	(7	)	$	3		$	(13	)	$	7
Portion of cost charged to expense	$	5		$	5		$	11		$	11		$	(2	)	$	3		$	(4	)	$	5