Derivative Financial Instruments (Financial Statement Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Collateral posted	$ 14	$ 12
Contractual Notional Amount	1,653	2,048
Unrecognized loss for all outstanding and terminated cash flow hedges included in accumulated other comprehensive income	249		$ 236
Cash Flow Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Contractual Notional Amount		425
Unrecognized loss for all outstanding and terminated cash flow hedges included in accumulated other comprehensive income	249	233
Total amount of amortization over the next twelve months for all cash flow hedges	14
Cash Flow Hedging [Member] | Expired hedge [Domain]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Notional Amount Expired	425
Settlement amount	24
Non-Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Contractual Notional Amount	$ 453	$ 388