Other Expenses (Restructuring Charges) (Details) - Other Expense [Member] - Severance - Unit Cost Initiative [Member] $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	$ 38	$ 35
Restructuring charges	11	22
Cash payments	(32)	(40)
Balance, end of period	17	17
Total restructuring charges incurred since inception of initiative	$ 57	$ 57