Fair Value Measurements (Non-Recurring Fair Value Measurements) (Details) - Non-recurring - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjustments To Assets Measured At Fair Value On Non Recurring Basis	$ (44)	$ (197)
Financing Receivables and Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjustments To Assets Measured At Fair Value On Non Recurring Basis	0	(23)
Cost and Equity Method Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjustments To Assets Measured At Fair Value On Non Recurring Basis	(9)	(115)
Long Lived Assets, Including Real Estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjustments To Assets Measured At Fair Value On Non Recurring Basis	(35)	$ (58)
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	0		$ 17
Level 2 | Financing Receivables and Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	0		0
Level 2 | Cost and Equity Method Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	0		0
Level 2 | Long Lived Assets, Including Real Estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	0		17
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	358		1,189
Level 3 | Financing Receivables and Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	0		30
Level 3 | Cost and Equity Method Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	0		103
Level 3 | Long Lived Assets, Including Real Estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Fair Value Disclosure	$ 358		$ 1,055