Debt (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Demand notes	$ 2,510	$ 2,581
Federal Home Loan Bank, advances	1,100	2,950
Securities sold under agreements to repurchase	79	0
Total short-term borrowings	3,689	5,531
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	11	0
Non-derivative cash collateral received from counterparties associated with repurchase agreements	0
Non-derivative noncash collateral received from counterparties associated with repurchase agreements	0	0
Unsecured debt
Short-term Debt [Line Items]
Demand notes	2,510	2,581
Federal Home Loan Bank, advances	0	0
Securities sold under agreements to repurchase	0	0
Total short-term borrowings	2,510	2,581
Secured debt
Short-term Debt [Line Items]
Demand notes	0	0
Federal Home Loan Bank, advances	1,100	2,950
Securities sold under agreements to repurchase	79	0
Total short-term borrowings	1,179	$ 2,950
Secured debt | Mortgage-backed residential | Maturity Less than 30 Days
Short-term Debt [Line Items]
Financial instruments sold under agreements to repurchase	$ 79