Severance and Restructuring Costs (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Employee Severance
Restructuring Reserve [Roll Forward]
Balance at January 1, 2018	$ 5
Accrued to expense	12
Payments, net	(12)
Balance at June 30, 2018	5
Restructuring Excluding Severance
Restructuring Reserve [Roll Forward]
Balance at January 1, 2018	4
Accrued to expense	46
Payments, net	(1)
Balance at June 30, 2018	$ 49