Derivative Instruments (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Total loss to be reclassified during next 12 months	$ 9
Margin cash collateral received from counterparties that was not offset against derivative assets	12	$ 16
Margin cash collateral provided to counterparties that was not offset against derivative assets or liabilities	238	$ 157
Interest Expense [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	6
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	$ 5

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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