Benefit Plans (Activity of Plan Assets with Significant Unobservable Fair Value Inputs) (Details) (Alternative Investments [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, beginning of year	$ 101	$ 98	$ 99
Actual return on plan assets	11	11	7
Purchases, sales and settlements	12	(8)	(8)
Fair value of plan assets, end of year	$ 124	$ 101	$ 98