Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 31	$ 28	$ 92	$ 84
Interest cost	21	21	64	63
Expected return on plan assets	(37)	(35)	(112)	(104)
Amortization of:
Net actuarial (gain) loss	13	13	40	37
Prior service credit	(5)	(5)	(15)	(15)
Special charges (credits)	3	(7)	3	(7)
Net periodic benefit cost (credit)	26	15	72	58
Employee Benefit Plans (Textual)
Contributions to benefit plans	80		104	132
Expected contributions to pension plans in current year	108		108
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	1	2	4	5
Interest cost	3	3	8	9
Expected return on plan assets	0	0	0	0
Amortization of:
Net actuarial (gain) loss	0	(1)	(2)	(1)
Prior service credit	(4)	(4)	(12)	(12)
Special charges (credits)	0	0	0	0
Net periodic benefit cost (credit)	$ 0	$ 0	(2)	1
Employee Benefit Plans (Textual)
Contributions to benefit plans			$ 17	$ 12