Assets and Liabilities with Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	$ 168	$ 131
Derivative Asset	[2]	302	392
Effect of Netting and Allocation of Collateral, Asset	[3],[4]	(1,221)	(975)
Margin Deposit Assets	[5]	343	221
Assets, Fair Value Disclosure		470	523
Derivative Liability	[2]	443	316
Effect of Netting and Allocation of Collateral, Liability	[3],[4]	(1,268)	(1,037)
Margin deposits posted with us by our counterparties	[5],[6]	52	4
Liabilities, Fair Value Disclosure		443	316
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	168	131
Effect of Netting and Allocation of Collateral, Asset	[3],[4]	(933)	(746)
Assets, Fair Value Disclosure		168	131
Effect of Netting and Allocation of Collateral, Liability	[3],[4]	(932)	(790)
Liabilities, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Effect of Netting and Allocation of Collateral, Asset	[3],[4]	(262)	(206)
Assets, Fair Value Disclosure		116	150
Effect of Netting and Allocation of Collateral, Liability	[3],[4]	(310)	(224)
Liabilities, Fair Value Disclosure		249	271
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
Effect of Netting and Allocation of Collateral, Asset	[3],[4]	(26)	(23)
Assets, Fair Value Disclosure		186	242
Effect of Netting and Allocation of Collateral, Liability	[3],[4]	(26)	(23)
Liabilities, Fair Value Disclosure		194	45
Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	[7]	550	592
Derivative Liability	[7]	769	529
Forward Contracts [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	[7]	0	0
Derivative Liability	[7]	0	0
Forward Contracts [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	[7]	338	327
Derivative Liability	[7]	549	461
Forward Contracts [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	[7]	212	265
Derivative Liability	[7]	220	68
Future [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		933	746
Derivative Liability		932	790
Future [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		933	746
Derivative Liability		932	790
Future [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		0	0
Derivative Liability		0	0
Future [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		0	0
Derivative Liability		0	0
Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		40	29
Derivative Liability		10	34
Interest Rate Contract [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		0	0
Derivative Liability		0	0
Interest Rate Contract [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		40	29
Derivative Liability		10	34
Interest Rate Contract [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		0	0
Derivative Liability		$ 0	$ 0

[1] As of December 31, 2018 and 2017, we had cash equivalents of $23 million and $21 million included in cash and cash equivalents and $145 million and $110 million included in restricted cash, respectively.

[2] At December 31, 2018 and 2017, we had $244 million and $155 million of collateral under master netting arrangements that were not offset against our derivative instruments on the Consolidated Balance Sheets primarily related to initial margin requirements.

[3] Cash collateral posted with (received from) counterparties allocated to level 1, level 2 and level 3 derivative instruments totaled $(1) million, $48 million and nil, respectively, at December 31, 2018. Cash collateral posted with (received from) counterparties allocated to level 1, level 2 and level 3 derivative instruments totaled $44 million, $18 million and nil, respectively, at December 31, 2017.

[4] We offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation; therefore, amounts recognized for the right to reclaim, or the obligation to return, cash collateral are presented net with the corresponding derivative instrument fair values. See Note 10 for further discussion of our derivative instruments subject to master netting arrangements.

[5] We offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation; therefore, amounts recognized for the right to reclaim, or the obligation to return, cash collateral are presented net with the corresponding derivative instrument fair values. See Note 10 for further discussion of our derivative instruments subject to master netting arrangements.

[6] At December 31, 2018 and 2017, $32 million and $2 million, respectively, were included in current and long-term derivative assets and liabilities and $20 million and $2 million, respectively, were included in other current liabilities on our Consolidated Balance Sheets.

[7] Includes OTC swaps and options.