Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Accrual Adjustments

	2017		2016		2015
	Millions
Compensation Cost included in Operation and Maintenance Expense	$	31	$	29	$	34
Income Tax Benefit Recognized in Consolidated Statement of Operations	$	13	$	12	$	14

Stock Options Activity

Changes in stock options for 2017 are summarized as follows:

	Options	Weighted Average Exercise Price		Weighted Average Remaining Years Contractual Term	Aggregate Intrinsic Value
Outstanding as of January 1, 2017	1,029,900	$	37.93
Exercised	654,200	$	40.02
Canceled/Forfeited	27,800	$	44.44
Outstanding as of December 31, 2017	347,900	$	33.49	1.9	$	6,265,679
Exercisable at December 31, 2017	347,900	$	33.49	1.9	$	6,265,679

Activity For Options Exercised

Activity for options exercised for the years ended December 31, 2017, 2016 and 2015 is shown below:

	2017		2016		2015
	Millions
Total Intrinsic Value of Options Exercised	$	5	$	7	$	3
Cash Received from Options Exercised	$	26	$	22	$	12
Tax Benefit Realized from Options Exercised	$	—	$	1	$	—

Restricted Stock Units Activity

Changes in restricted stock units for the year ended December 31, 2017 are summarized as follows:

	Shares	Weighted Average Grant Date Fair Value		Weighted Average Remaining Years Contractual Term	Aggregate Intrinsic Value
Non-vested as of January 1, 2017	322,196	$	38.75
Granted	212,158	$	44.33
Vested	303,092	$	39.96
Canceled/Forfeited	17,363	$	41.76
Non-vested as of December 31, 2017	213,899	$	42.32	1.0	$	11,015,850

Performance Units Information

Changes in performance share units for the year ended December 31, 2017 are summarized as follows:

	Shares	Weighted Average Grant Date Fair Value		Weighted Average Remaining Years Contractual Term	Aggregate Intrinsic Value
Non-vested as of January 1, 2017	393,812	$	44.20
Granted	382,830	$	45.02
Vested	402,451	$	44.03
Canceled/Forfeited	41,730	$	44.69
Non-vested as of December 31, 2017	332,461	$	45.29	1.7	$	17,121,742