Restructuring - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Restructuring Cost and Reserve [Line Items]
Pre-tax charge	$ 229	$ 229
Severance and employee related costs	207
Reserve balance	222	222	$ 0	$ 0
Other Accrued Liabilities
Restructuring Cost and Reserve [Line Items]
Reserve balance	172	172
Other Noncurrent Liabilities
Restructuring Cost and Reserve [Line Items]
Reserve balance	50	50
Reduction in Workforce
Restructuring Cost and Reserve [Line Items]
Severance and employee related costs	117
Business Process Initiatives
Restructuring Cost and Reserve [Line Items]
Severance and employee related costs	90
Minimum
Restructuring Cost and Reserve [Line Items]
Expected total pre-tax charges	270	270
Maximum
Restructuring Cost and Reserve [Line Items]
Expected total pre-tax charges	$ 290	$ 290