Pension and Other Postretirement Benefits - Assumptions and 401(k) Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Benefit payments including expected future services [Abstract]
Expense for matching contributions in the 401K plan	$ 98,000,000	$ 91,000,000	$ 78,000,000
Pension Benefits [Member]
Assumptions for pension and other postretirement benefits [Abstract]
Discount rate: Benefit obligation	3.75%	4.50%
Discount rate: Benefit cost	4.50%	3.50%
Expected long-term return on plan assets: Benefit cost	7.25%	8.00%
Recognition Period For Market Fluctuation Impacts On Pension Cost	5 years
Defined Benefit Plan Market Related Value Of Pension Plan Assets	3,900,000,000
Defined Benefit Plan Market Value Of Pension Plan Assets	4,200,000,000
Benefit payments including expected future services [Abstract]
Paid after one year	399,000,000
Paid after two years	334,000,000
Paid after three years	336,000,000
Paid after four years	337,000,000
Paid after five years	338,000,000
Paid in six to ten years	1,631,000,000
Other Postretirement Benefits [Member]
Assumptions for pension and other postretirement benefits [Abstract]
Discount rate: Benefit obligation	3.50%	4.00%
Discount rate: Benefit cost	4.00%	3.25%
Expected long-term return on plan assets: Benefit cost	5.00%	5.00%
Benefit payments including expected future services [Abstract]
Paid after one year	31,000,000
Paid after two years	30,000,000
Paid after three years	29,000,000
Paid after four years	28,000,000
Paid after five years	27,000,000
Paid in six to ten years	$ 115,000,000