Cost Reduction Programs and Other Charges - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) employee	Mar. 31, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	$ 131	$ 89
Cost reduction programs and other charges, after-tax and noncontrolling interest	95	81
Cost reduction program charges	78
Cost reduction program charges, net of tax	$ 56
Number of positions expected to be eliminated | employee	600
Number of positions eliminated | employee	450
Other charges, merger related		56
Other charges, merger related, net of tax	$ 39	53
Cash requirement for the cost reduction program and other charges	74
Payments made through September 30, 2019	64
Severance costs
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges		33
Cost reduction programs and other charges, after-tax and noncontrolling interest		$ 28
Merger-related and other charges
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	53
Payments made through September 30, 2019	36
Cost Reduction Program
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	78
Payments made through September 30, 2019	28
Cost Reduction Program | Severance costs
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	58
Payments made through September 30, 2019	24
Cost Reduction Program | Other cost reduction charges
Restructuring Cost and Reserve [Line Items]
Cost reduction programs and other charges	20
Payments made through September 30, 2019	$ 4