Retirement Benefits (Unaudited) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Defined contribution plan, employer contributions	$ 73	$ 75
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost	114	129
Interest cost	315	279
Expected return on plan assets	(467)	(453)
Amortization of:
Prior service cost (credit)	(15)	(14)
Net loss from previous years	82	152
Net periodic benefit cost	29	93
Employer Contributions
Defined benefit plan, employer contributions	21
Medical and Life Benefits
Components of Net Periodic Benefit Cost
Service cost	8	9
Interest cost	26	24
Expected return on plan assets	(21)	(19)
Amortization of:
Prior service cost (credit)	(7)	(12)
Net loss from previous years	2	7
Net periodic benefit cost	8	9
Employer Contributions
Defined benefit plan, employer contributions	$ 7