Retirement Benefits - Fair Value Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Cash equivalents	$ 518	[1]	$ 1,230	[1]

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