Retirement Plan Benefits - Pension Plan Investments at Fair Value Represented 5% or More of Pension Plan Net Assets (Details) (Pension Plan Net Assets, Credit Concentration Risk, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	$ 421	$ 385
EB Daily Valued Small Cap Stock Index Fund
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	30	30
EB Daily Valued Stock Index Fund
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	103	104
EB Daily Valued International Stock Index Fund
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	27	30
EB Long Term Government Bond Index
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	50	40
EB Long Term Credit Bond Index
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	74	63
Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	0	118
Custom Long Duration Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan investments, at fair value	$ 137	$ 0