Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	$ 22	[1]	$ 29	[1]
Amortization of:
Pension and Other Postretirement Benefit Expense	159		173
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	82	[2]	69	[2]
Interest cost	178	[2]	183	[2]
Expected return on assets	(257)	[2]	(241)	[2]
Amortization of:
Prior service cost (benefit)	3	[2]	3	[2]
Actuarial loss	143	[2]	105	[2]
Net periodic benefit cost	149	[2]	119	[2]
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	30	[2]	33	[2]
Interest cost	42	[2]	55	[2]
Expected return on assets	(38)	[2]	(38)	[2]
Amortization of:
Prior service cost (benefit)	(43)	[2]	(4)	[2]
Actuarial loss	20	[2]	8	[2]
Net periodic benefit cost	11	[2]	54	[2]
CENG [Member] | Pension Plan, Defined Benefit [Member]
Amortization of:
Pension and Other Postretirement Benefit Costs	3
CENG [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Amortization of:
Pension and Other Postretirement Benefit Costs	3
CENG [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	$ 2	[1]			$ 1

[1] (a)Includes $2 million related to CENG for the three months ended March 31, 2015. CENG is not included in the 2014 amounts.

[2] (a)For the three months ended March 31, 2015, the cost for pension benefits and other postretirement benefits related to CENG were $3 million and $3 million, respectively. CENG is not included in the 2014 amounts.