Derivatives - Offsetting Derivative Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative Fair Value Gross Amount Assets Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	$ 1,700	$ 1,114
Derivative, Collateral, Obligation to Return Cash	(346)	(271)
Derivative Fair Value Gross Amount Liabilities Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	1,202	874
Assets
Derivative Fair Value Gross Amount Assets Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	1,686	1,107
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(507)	(410)
Derivative, Collateral, Obligation to Return Cash	(468)	(348)
Derivative, Fair Value, Amount Offset Against Collateral, Net	711	349
Liability
Derivative Fair Value Gross Amount Liabilities Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	1,202	874
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(507)	(410)
Derivative, Collateral, Right to Reclaim Cash	(472)	(123)
Derivative Fair Value Amount Offset Against Collateral Net	223	341
Derivative \| Assets
Derivative Fair Value Gross Amount Assets Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	1,686	1,107
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(507)	(410)
Derivative, Collateral, Obligation to Return Cash	(468)	(348)
Derivative, Fair Value, Amount Offset Against Collateral, Net	711	349
Derivative \| Liability
Derivative Fair Value Gross Amount Liabilities Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	1,202	874
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(507)	(410)
Derivative, Collateral, Right to Reclaim Cash	(472)	(123)
Derivative Fair Value Amount Offset Against Collateral Net	$ 223	$ 341

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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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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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