Cost Reduction Programs and Other Charges - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) employee	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) employee	Jun. 30, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	$ 141	$ 24	$ 230	$ 43
Cost reduction programs and other charges, after-tax and noncontrolling interest	113	$ 21	194	$ 39
Cost reduction program charges	76		109
Cost reduction program charges, net of tax	$ 61		$ 89
Number of positions expected to be eliminated | employee			1,100
Number of positions eliminated | employee	700		700
Other charges, merger related	$ 65		$ 121
Other charges, merger related, net of tax	52		105
Cash requirement for the cost reduction program and other charges	225		225
Payments made through June 30, 2019			135
Severance costs
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	42		51
Payments made through June 30, 2019			37
Other cost reduction charges
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	$ 34		58
Payments made through June 30, 2019			$ 21