Retirement Benefits and Trusteed Assets (Pension Plan - Fair Value Measurement using Level 3 Inputs) (Details) (Pension Plan [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Change in plan assets
Plan assets at fair value, beginning of year	$ 2,632	$ 2,211
Actual return on plan assets	212	316
Plan assets at fair value, end of year	2,812	2,632
Hedge Funds and Similar Investments [Member]
Change in plan assets
Plan assets at fair value, end of year	546	528
Private Equity and Other [Member]
Change in plan assets
Plan assets at fair value, end of year	135	122
Level 3 [Member]
Change in plan assets
Plan assets at fair value, beginning of year	407	363
Actual return on plan assets	27	31
Purchases	38	33
Sales	(22)	(20)
Plan assets at fair value, end of year	450	407
The amount of total gains for the period attributable to the change in unrealized gains or losses related to assets still held at the end of the period	23	29
Level 3 [Member] | Hedge Funds and Similar Investments [Member]
Change in plan assets
Plan assets at fair value, beginning of year	285	238
Actual return on plan assets	15	29
Purchases	16	18
Sales	(1)	0
Plan assets at fair value, end of year	315	285
The amount of total gains for the period attributable to the change in unrealized gains or losses related to assets still held at the end of the period	15	27
Level 3 [Member] | Private Equity and Other [Member]
Change in plan assets
Plan assets at fair value, beginning of year	122	125
Actual return on plan assets	12	2
Purchases	22	15
Sales	(21)	(20)
Plan assets at fair value, end of year	135	122
The amount of total gains for the period attributable to the change in unrealized gains or losses related to assets still held at the end of the period	$ 8	$ 2