Exit Costs - Summary of expenses incurred to date (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	$ 8			$ 0	$ 49	$ 0
Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	5	$ 8	$ 17		30
Cumulative costs recognized in prior year					0
Estimate of remaining costs	8				8
Program expected costs	38				38
Reorganization | Noncontrolling Interest
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year					5
Program expected costs	8				8
PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	3	8	8		19
Cumulative costs recognized in prior year					41
Estimate of remaining costs	30				30
Program expected costs	90				90
Severance and Termination Benefits | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	4	4	17		25
Cumulative costs recognized in prior year					0
Estimate of remaining costs	5				5
Program expected costs	30				30
Severance and Termination Benefits | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	3	4	4		11
Cumulative costs recognized in prior year					22
Estimate of remaining costs	5				5
Program expected costs	38				38
Facility Exit Costs | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	2	0		2
Cumulative costs recognized in prior year					0
Estimate of remaining costs	1				1
Program expected costs	3				3
Facility Exit Costs | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0	4		4
Cumulative costs recognized in prior year					0
Estimate of remaining costs	18				18
Program expected costs	22				22
Contract Termination & Other Costs | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	1	0	0		1
Cumulative costs recognized in prior year					0
Estimate of remaining costs	0				0
Program expected costs	1				1
Contract Termination & Other Costs | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	8	0		8
Cumulative costs recognized in prior year					4
Estimate of remaining costs	7				7
Program expected costs	19				19
Non-Cash Charges & Impairments | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	2	0		2
Cumulative costs recognized in prior year					0
Estimate of remaining costs	2				2
Program expected costs	4				4
Non-Cash Charges & Impairments | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	$ (4)	$ 0		(4)
Cumulative costs recognized in prior year					15
Estimate of remaining costs	0				0
Program expected costs	$ 11				$ 11