Employee Benefit Plans, Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Benefit Plans (Textual)
The percentage of the higher of the projected benefit obligation or market-related value of plan assets in excess of which net actuarial losses are amortized	10.00%
Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	$ 123	$ 111	$ 109
Interest cost	86	84	98
Expected return on plan assets	(150)	(139)	(133)
Amortization of:
Net actuarial (gain) loss	53	49	62
Prior service credit	(20)	(20)	(22)
Special charges (credits)	4	(7)	7
Net periodic benefit cost (credit)	96	78	121
Other Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	6	7	8
Interest cost	10	12	14
Expected return on plan assets	0	0	0
Amortization of:
Net actuarial (gain) loss	(3)	(1)	0
Prior service credit	(16)	(16)	(18)
Special charges (credits)	0	0	0
Net periodic benefit cost (credit)	$ (3)	$ 2	$ 4