Restructuring Costs - Narrative (Details) $ in Millions	Dec. 31, 2017 USD ($)
Fiscal 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	$ 221
Fiscal 2017 Plan | Employee severance
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	214
Fiscal 2017 Plan | Facilities costs
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	7
Fiscal 2016 Plan
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	58
Fiscal 2016 Plan | Employee severance
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	25
Fiscal 2016 Plan | Facilities costs
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	33
Fiscal 2015 Plan
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	228
Fiscal 2015 Plan | Employee severance
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	220
Fiscal 2015 Plan | Facilities costs
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	$ 8