Reconciliation of Changes in Fair Value of Financial Assets and Liabilities Classified as Level Three In Fair Value Hierarchy (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance					$ 26
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value			$ (75)	$ (308)	(384)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			(33)	(214)	(419)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(39)
Liability Settlements			220	290	45
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3					0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3			0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3			46	0	3
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)			13	(140)	(373)
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities			9	8
Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3				0	0
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance			0	0	39
Included in earnings			0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(39)
Settlements			0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			0	0	0
Ending Balance			0	0	0
Change in unrealized gains (losses) relating to investments and derivatives still held			0	0	0
Stock Compensation Plan [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3					0
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value					(381)	$ (8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings					(381)
Liability Settlements					5
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	$ 46	$ 3	46	0	3
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)				(143)	(375)
Derivatives [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value			(75)	(308)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			(33)	(217)
Liability Settlements			220	290
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)			13
Stock Compensation Plan [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value			0	0	(3)	$ (5)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			0	3	(38)
Liability Settlements			0	0	40
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3			0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3			0	0	0
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)			0	3	$ 2
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities			$ 0	$ 0