Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 28	$ 27
Interest cost	21	24
Expected return on plan assets	(35)	(33)
Amortization of:
Prior service credit	(5)	(5)
Net actuarial loss	12	16
Net periodic benefit cost	21	29
Employee Benefit Plans (Textual)
Contributions to benefit plans	8	7
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	2	2
Interest cost	3	4
Expected return on plan assets	0	0
Amortization of:
Prior service credit	(4)	(5)
Net actuarial loss	0	0
Net periodic benefit cost	1	1
Employee Benefit Plans (Textual)
Contributions to benefit plans	$ 4	$ 2