Restructuring and Asset Impairment Charges (Schedule of Restructuring Charges) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restructuring Reserve [Roll Forward]
Charged to Costs and Expenses	$ 1	$ 2
Restructuring costs incurred to date	351
2020-2021 Cost Savings Restructuring Program
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance	5
Charged to Costs and Expenses	0
Payments and Other	(2)
Ending Reserve Balance	3
Restructuring costs incurred to date	16
2020-2021 Cost Savings Restructuring Program | Branch closure charges
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance	3
Charged to Costs and Expenses	0
Payments and Other	(1)
Ending Reserve Balance	2
Restructuring costs incurred to date	8
2020-2021 Cost Savings Restructuring Program | Severance and other
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance	2
Charged to Costs and Expenses	0
Payments and Other	(1)
Ending Reserve Balance	1
Restructuring costs incurred to date	$ 8