Retirement Plans and Other Benefits (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		7 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended
	Jul. 31, 2012	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Pension Benefits	Jun. 30, 2013 Pension Benefits	Jun. 30, 2014 Pension Benefits	Jun. 30, 2013 Pension Benefits	Jul. 31, 2014 Pension Benefits	Jun. 30, 2014 Pension Benefits Expected contributions	Jun. 30, 2014 Pension Benefits Expected contributions Maximum	Jun. 30, 2014 Other Benefits	Jun. 30, 2013 Other Benefits	Jun. 30, 2014 Other Benefits	Jun. 30, 2013 Other Benefits	Jun. 30, 2014 Other Benefits Expected contributions
Retirement Plans and Other Benefits
Regulatory asset amortization period	3 years
Amortization of regulatory assets		$ 2	$ 2	$ 4	$ 4
Net periodic benefit costs and the portion of these costs charged to expense
Service cost - benefits earned during the period						12	15	27	32				5	6	9	12
Interest cost on benefit obligation						33	28	65	56				11	10	23	20
Expected return on plan assets						(39)	(36)	(79)	(73)				(13)	(12)	(25)	(23)
Amortization of prior service cost									1
Amortization of net actuarial loss						3	10	5	20					3		6
Net periodic benefit cost						9	17	18	36				3	7	7	15
Portion of cost charged to expense						5	9	11	19				3	4	5	9
Contributions
Employer's contributions under the plan										140
Minimum Contributions under MAP-21
Minimum contributions under MAP-21								141
2014								0
2015								19
2016								122
Expected employer's contributions
Expected employer's contributions												300
2014											175						10
2015												100					10
2016												$ 25					$ 10