Restructuring Charges (Schedule of Changes in Restructuring Reserves) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		$ 15	$ 18	$ 0
Restructuring charges		53	45	93
Payments		(58)	(43)	(72)
Adjustments for non-cash charges			(5)	(3)
Balance at end of period		10	15	18
Total restructuring charges incurred to date	[1]	191
Employee costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		8	10	0
Restructuring charges		10	10	52
Payments		(13)	(12)	(44)
Adjustments for non-cash charges	[2]		0	(2)
Balance at end of period		5	8	10
Total restructuring charges incurred to date	[1]	72
Facilities costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		0	4	0
Restructuring charges		4	2	15
Payments		(3)	(6)	(6)
Adjustments for non-cash charges	[2]		0	(5)
Balance at end of period		1	0	4
Total restructuring charges incurred to date	[1]	21
Technology costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		6	0	0
Restructuring charges		37	26	0
Payments		(39)	(15)	0
Adjustments for non-cash charges	[2]		(5)	0
Balance at end of period		4	6	0
Total restructuring charges incurred to date	[1]	63
Other costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning of period		1	4	0
Restructuring charges		2	7	26
Payments		(3)	(10)	(22)
Adjustments for non-cash charges	[2]		0	0
Balance at end of period		0	$ 1	$ 4
Total restructuring charges incurred to date	[1]	$ 35

[1] Restructuring activities were completed as of 12/31/2018.

[2] Adjustments for non-cash charges primarily relate to impairments of previously capitalized software costs in Technology Costs.