Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Plan [Member]
Components of net periodic benefit cost:
Service cost	$ 27	$ 30
Interest cost	24	23
Expected return on plan assets	(33)	(33)
Amortization of:
Prior service credit	(5)	(5)
Net actuarial loss	16	8
Net periodic benefit cost	29	23
Employee Benefit Plans (Textual)
Contributions to benefit plans	7	10
Other Postretirement Benefit Plan [Member]
Components of net periodic benefit cost:
Service cost	2	2
Interest cost	4	4
Expected return on plan assets	0	0
Amortization of:
Prior service credit	(5)	(5)
Net actuarial loss	0	0
Net periodic benefit cost	1	1
Employee Benefit Plans (Textual)
Contributions to benefit plans	$ 2	$ 4