Debt (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Demand notes	$ 2,581	$ 2,477
Federal Home Loan Bank, advances	2,950	6,825
Securities sold under agreements to repurchase	0	685
Total short-term borrowings	$ 5,531	$ 9,987
Weighted Average Interest Rate	1.80%	2.50%
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	$ 0	$ 0
Non-derivative cash collateral received from counterparties associated with repurchase agreements	0	8
Non-derivative noncash collateral received from counterparties associated with repurchase agreements	0	4
Unsecured debt
Short-term Debt [Line Items]
Demand notes	2,581	2,477
Federal Home Loan Bank, advances	0	0
Securities sold under agreements to repurchase	0	0
Total short-term borrowings	2,581	2,477
Secured debt
Short-term Debt [Line Items]
Demand notes	0	0
Federal Home Loan Bank, advances	2,950	6,825
Securities sold under agreements to repurchase	0	685
Total short-term borrowings	2,950	$ 7,510
Financial instruments sold under agreements to repurchase	$ 0