Retirement Benefits - Fair Value Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fair Value Defined Benefit Plan Measured On Recurring Basis Financial Statement Captions [Line Items]
Cash equivalents	$ 1	[1]	$ 995	[1]

[1] Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.