Debt (Schedule of Short-term Debt) (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Demand notes	$ 2,532,000,000	$ 2,581,000,000
Federal Home Loan Bank, advances	500,000,000	2,950,000,000
Total short-term borrowings	3,032,000,000	5,531,000,000
Unsecured debt
Short-term Debt [Line Items]
Demand notes	2,532,000,000	2,581,000,000
Federal Home Loan Bank, advances	0	0
Total short-term borrowings	2,532,000,000	2,581,000,000
Secured debt
Short-term Debt [Line Items]
Demand notes	0	0
Federal Home Loan Bank, advances	500,000,000	2,950,000,000
Total short-term borrowings	$ 500,000,000	$ 2,950,000,000