Restructuring Costs - Analysis of the Cost for Restructuring (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 0	$ 31	$ 0	$ 85
Operating Segments [Member] | HCB [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		1		2
Operating Segments [Member] | CRB [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		25		64
Operating Segments [Member] | IRR [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		2		7
Operating Segments [Member] | BDA [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		0		0
Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		3		12
Termination benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		6		19
Termination benefits [Member] | Operating Segments [Member] | HCB [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		0		0
Termination benefits [Member] | Operating Segments [Member] | CRB [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		5		14
Termination benefits [Member] | Operating Segments [Member] | IRR [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		0		3
Termination benefits [Member] | Operating Segments [Member] | BDA [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		0		0
Termination benefits [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		1		2
Professional services and other [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		25		66
Professional services and other [Member] | Operating Segments [Member] | HCB [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		1		2
Professional services and other [Member] | Operating Segments [Member] | CRB [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		20		50
Professional services and other [Member] | Operating Segments [Member] | IRR [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		2		4
Professional services and other [Member] | Operating Segments [Member] | BDA [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		0		0
Professional services and other [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs		$ 2		$ 10