Exit Costs - Summary of expenses incurred to date (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	$ 0		$ 4	$ 0	$ 13
PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	$ 2		2
Cumulative costs recognized in prior years						$ 68
Estimate of remaining costs	18			18
Total Exit and disposal costs	88			88
Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	2		2
Cumulative costs recognized in prior years						35
Estimate of remaining costs	1			1
Total Exit and disposal costs	38			38
Less: Exit and disposal costs related to discontinued operations	25			25
Total Exit and disposal costs related to continuing operations	13			13
Severance and Termination Benefits | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						34
Estimate of remaining costs	0			0
Total Exit and disposal costs	34			34
Severance and Termination Benefits | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	1		1
Cumulative costs recognized in prior years						30
Estimate of remaining costs	1			1
Total Exit and disposal costs	32			32
Less: Exit and disposal costs related to discontinued operations	19			19
Total Exit and disposal costs related to continuing operations	13			13
Facility Exit Costs | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						6
Estimate of remaining costs	16			16
Total Exit and disposal costs	22			22
Facility Exit Costs | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						2
Estimate of remaining costs	0			0
Total Exit and disposal costs	2			2
Less: Exit and disposal costs related to discontinued operations	2			2
Total Exit and disposal costs related to continuing operations	0			0
Contract Termination & Other Costs | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	2		2
Cumulative costs recognized in prior years						17
Estimate of remaining costs	2			2
Total Exit and disposal costs	21			21
Contract Termination & Other Costs | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						1
Estimate of remaining costs	0			0
Total Exit and disposal costs	1			1
Less: Exit and disposal costs related to discontinued operations	1			1
Total Exit and disposal costs related to continuing operations	0			0
Non-Cash Charges & Impairments | PLS exit program
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						11
Estimate of remaining costs	0			0
Total Exit and disposal costs	11			11
Non-Cash Charges & Impairments | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	$ 1		1
Cumulative costs recognized in prior years						$ 2
Estimate of remaining costs	0			0
Total Exit and disposal costs	3			3
Less: Exit and disposal costs related to discontinued operations	3			3
Total Exit and disposal costs related to continuing operations	$ 0			$ 0