Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 31	$ 28
Interest cost	21	21
Expected return on plan assets	(37)	(35)
Amortization of:
Net actuarial (gain) loss	13	12
Prior service credit	(5)	(5)
Net periodic benefit cost	23	21
Employee Benefit Plans (Textual)
Contributions to benefit plans	7	8
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	1	2
Interest cost	3	3
Expected return on plan assets	0	0
Amortization of:
Net actuarial (gain) loss	(1)	0
Prior service credit	(4)	(4)
Net periodic benefit cost	(1)	1
Employee Benefit Plans (Textual)
Contributions to benefit plans	$ 5	$ 4