Restructuring Reserves (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Restructuring Reserve [Roll Forward]
Beginning balance	$ 76
Costs incurred	57	[1]
Reserves reversed	(6)	[2]
Payments	(46)
Ending balance	81
Restructuring and Related Costs, Other Costs (Income), Net	11
Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	30
Costs incurred	29
Reserves reversed	(5)	[2]
Payments	(23)
Ending balance	$ 31
Restructuring Reserve, Expected Final Year of Payments	2018
Abandonment of Excess Facilities [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	$ 40
Costs incurred	20
Reserves reversed	(1)	[2]
Payments	(14)
Ending balance	$ 45
Restructuring Reserve, Expected Final Year of Payments	2027
Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	$ 6	[3]
Costs incurred	8	[3]
Payments	(9)	[3]
Ending balance	$ 5	[3]
Restructuring Reserve, Expected Final Year of Payments	2018

[1] Excludes $11 million of charges, net, primarily associated with litigation-related matters, hurricane response costs, and non-cash compensation due at an acquired business.

[2] Represents reductions in cost of plans.

[3] Other includes relocation and moving expenses associated with facility consolidations, as well as employee retention costs which are accrued ratably over the period through which employees must work to qualify for a payment.