Income Taxes Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes Summary [Line Items]
Income Tax Expense (Benefit)	$ (190)	$ (4,463)	$ 1,144
Income Tax Effects Allocated Directly to Equity, Equity Transactions	165
Income Tax Effects Allocated Directly to Equity, Other	(10)
Other Comprehensive Income (Loss), Tax	4
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	(31)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	1,423	2,727	74
Deferred Tax Assets, Operating Loss Carryforwards	2,587	1,556
Deferred Tax Assets, Gross	4,690	4,122
Deferred Tax Assets, Valuation Allowance	4,389	2,949
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	1,440
Income Tax Effects Allocated Directly to Equity	$ 17
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	5.00%
Percentage Of Beneficial Interest Owned	50.00%
Treasury Regulations Purchase of Stock	5.00%
Unrecognized Tax Benefits	$ 202	280	$ 303	$ 644
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	20	20
Domestic Tax Authority [Member]
Income Taxes Summary [Line Items]
Tax Credit Carryforward, Amount	6,200
Deferred Tax Assets, Operating Loss Carryforwards	2,161
State and Local Jurisdiction [Member]
Income Taxes Summary [Line Items]
Tax Credit Carryforward, Amount	9,500
Deferred Tax Assets, Operating Loss Carryforwards	426
Unrecognized Tax Benefits	$ 76	$ 44