Other Expenses (Restructuring Charges) (Details) - Other Expense [Member] - Severance - Unit Cost Initiative [Member] $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	$ 17	$ 35
Restructuring charges	3	25
Cash payments	(3)	(43)
Balance, end of period	17	17
Total restructuring charges incurred since inception of initiative	$ 60	$ 60