Benefit Plans (Projected Benefit Obligations, Plan Assets and Funded Status of Pension Plans) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year	$ 7,077	$ 6,167
Pension [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	7,924	6,965
Service cost	86	79	74
Interest cost	314	344	351
Benefits paid	(410)	(420)
Actuarial losses	(784)	956
Other	7	0
Accrued postretirement health care costs at end of year	7,137	7,924	6,965
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	6,167	5,275
Actual return on plan assets	927	755
Employer contributions	393	557
Benefits paid	(410)	(420)
Fair value of plan assets at end of year	7,077	6,167	5,275
Net pension liability recognized at December 31	$ (60)	$ (1,757)