Fair Value Measurements (Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	9.50%
Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	16.50%
Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Individually Insignificant Recurring Fair Value Measurements	$ 4	$ 32
Individually Insignificant Nonrecurring Fair Value Measurements	11	80
Level 3 | Recurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	4,141	4,042	$ 4,057	$ 4,034	$ 4,020	$ 4,175
Level 3 | Recurring | US Corporate | Income Approach
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 885	$ 834
Level 3 | Recurring | US Corporate | Income Approach | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	1.40%	1.70%
Level 3 | Recurring | US Corporate | Income Approach | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	17.40%	14.10%
Level 3 | Recurring | US Corporate | Income Approach | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	7.60%	8.60%
Level 3 | Recurring | Mortgage and asset-backed | Income Approach
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 8	$ 31
Level 3 | Recurring | Mortgage and asset-backed | Income Approach | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	2.80%	5.00%
Level 3 | Recurring | Mortgage and asset-backed | Income Approach | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	7.00%	12.00%
Level 3 | Recurring | Mortgage and asset-backed | Income Approach | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	4.90%	10.50%
Level 3 | Recurring | Corporate - non-U.S. | Income Approach
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure		$ 236
Level 3 | Recurring | Corporate - non-U.S. | Income Approach | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate		6.50%
Level 3 | Recurring | Corporate - non-U.S. | Income Approach | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate		14.00%
Level 3 | Recurring | Corporate - non-U.S. | Income Approach | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate		7.50%
Level 3 | Recurring | Other financial assets
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 3,244	$ 2,637
Level 3 | Recurring | Other financial assets | Income Approach, Market Comparables
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure		$ 259
Level 3 | Recurring | Other financial assets | Income Approach, Market Comparables | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
EBITDA Multiple		6.1
Capitalization Rate		7.80%
Level 3 | Recurring | Other financial assets | Income Approach, Market Comparables | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
EBITDA Multiple		15
Capitalization Rate		7.80%
Level 3 | Recurring | Other financial assets | Income Approach, Market Comparables | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
EBITDA Multiple		9.9
Capitalization Rate		7.80%
Level 3 | Non-recurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	230	$ 436
Assets Fair Value Disclosure Nonrecurring	148	122
Level 3 | Non-recurring | Financing receivables and loans held for sale | Income Approach
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 31	$ 146
Level 3 | Non-recurring | Financing receivables and loans held for sale | Income Approach | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	9.00%	6.50%
Level 3 | Non-recurring | Financing receivables and loans held for sale | Income Approach | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	30.00%	30.00%
Level 3 | Non-recurring | Financing receivables and loans held for sale | Income Approach | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	20.40%	10.70%
Level 3 | Non-recurring | Cost and equity method investments | Income Approach
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 132	$ 293
Level 3 | Non-recurring | Cost and equity method investments | Income Approach | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	9.00%	9.50%
Level 3 | Non-recurring | Cost and equity method investments | Income Approach | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	20.00%	35.00%
Level 3 | Non-recurring | Cost and equity method investments | Income Approach | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	13.30%	14.40%
Level 3 | Non-recurring | Long Lived Assets | Income Approach
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 620	$ 830
Level 3 | Non-recurring | Long Lived Assets | Income Approach | Lower Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	2.50%	1.80%
Level 3 | Non-recurring | Long Lived Assets | Income Approach | Upper Limit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	11.60%	11.70%
Level 3 | Non-recurring | Long Lived Assets | Income Approach | Weighted average
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Discount Rate	10.40%	10.50%