Fair Value Disclosures (Quantitative Information about and Sensitivity of Significant Unobservable Inputs Used in Recurring Level 3 Fair Value Measurements) (Details) - Recurring - Level 3 $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2015 USD ($) $ / MWh $ / PowerCapacityUnit	Dec. 31, 2014 USD ($) $ / MWh $ / PowerCapacityUnit
Residential Mortgage-backed Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 404	$ 175
Residential Mortgage-backed Securities \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - higher (lower)	0.00%	3.00%
Residential Mortgage-backed Securities \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - higher (lower)	80.00%	90.00%
Residential Mortgage-backed Securities \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)	36.00%	15.00%
Commercial Mortgage-backed Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 79	$ 96
Commercial Mortgage-backed Securities \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - higher (lower)	0.00%	0.00%
Commercial Mortgage-backed Securities \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - higher (lower)	9.00%	7.00%
Commercial Mortgage-backed Securities \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)	2.00%	1.00%
Asset-backed Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets		$ 76
Asset-backed Securities \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - higher (lower)		0.00%
Asset-backed Securities \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - higher (lower)		62.00%
Asset-backed Securities \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)		23.00%
Corporate Bonds
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 226	$ 386
Liabilities		$ 78
Corporate Bonds \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - higher (lower)	4.00%	1.00%
Corporate Bonds \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - higher (lower)	119.00%	160.00%
Corporate Bonds \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)	83.00%	90.00%
Corporate Bonds \| Option Model
Fair Value Inputs
At the Money Volatility		10.00%
Volatility Skew		(1.00%)
Corporate Bonds \| Option Model \| Weighted Average
Fair Value Inputs
At the Money Volatility		10.00%
Volatility Skew		(1.00%)
Collateralized Debt and Loan Obligations
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 545	$ 1,152
Collateralized Debt and Loan Obligations \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - higher (lower)	45.00%	20.00%
Collateralized Debt and Loan Obligations \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - higher (lower)	103.00%	100.00%
Collateralized Debt and Loan Obligations \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)	77.00%	66.00%
Collateralized Debt and Loan Obligations \| Correlation Model \| Minimum
Fair Value Inputs
Credit Correlation	35.00%	47.00%
Collateralized Debt and Loan Obligations \| Correlation Model \| Maximum
Fair Value Inputs
Credit Correlation	60.00%	65.00%
Collateralized Debt and Loan Obligations \| Correlation Model \| Weighted Average
Fair Value Inputs
Credit Correlation	49.00%	56.00%
Loans and Lending Commitments
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 5,164	$ 5,874
Loans and Lending Commitments \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Loan Price	40.00%	15.00%
Loans and Lending Commitments \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Loan Price	103.00%	105.00%
Loans and Lending Commitments \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Loan Price	89.00%	89.00%
Loans and Lending Commitments \| Discounted Cash Flow \| Minimum
Fair Value Inputs
Implied Weighted Average Cost of Capital	6.00%
Capitalization Rate	4.00%
Loans and Lending Commitments \| Discounted Cash Flow \| Maximum
Fair Value Inputs
Implied Weighted Average Cost of Capital	8.00%
Capitalization Rate	10.00%
Loans and Lending Commitments \| Discounted Cash Flow \| Weighted Average
Fair Value Inputs
Implied Weighted Average Cost of Capital	7.00%
Capitalization Rate	4.00%
Loans and Lending Commitments \| Corporate Loan Model \| Minimum
Fair Value Inputs
Credit Spread	0.72%	0.36%
Loans and Lending Commitments \| Corporate Loan Model \| Maximum
Fair Value Inputs
Credit Spread	8.31%	7.53%
Loans and Lending Commitments \| Corporate Loan Model \| Weighted Average
Fair Value Inputs
Credit Spread	5.44%	3.73%
Loans and Lending Commitments \| Margin Loan Model \| Minimum
Fair Value Inputs
Discount Rate	2.00%	2.00%
Credit Spread	0.80%	1.50%
Volatility Skew	14.00%	3.00%
Loans and Lending Commitments \| Margin Loan Model \| Maximum
Fair Value Inputs
Discount Rate	6.00%	3.00%
Credit Spread	5.48%	4.51%
Volatility Skew	70.00%	37.00%
Loans and Lending Commitments \| Margin Loan Model \| Weighted Average
Fair Value Inputs
Discount Rate	4.00%	3.00%
Credit Spread	1.65%	2.16%
Volatility Skew	36.00%	21.00%
Loans and Lending Commitments \| Option Model
Fair Value Inputs
Volatility Skew	(1.00%)	(1.00%)
Loans and Lending Commitments \| Option Model \| Weighted Average
Fair Value Inputs
Volatility Skew	(1.00%)	(1.00%)
Other Debt
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 530	$ 285
Other Debt \| Comparable Pricing
Fair Value Inputs
Comparable Bond Price - higher (lower)	11.00%	15.00%
Other Debt \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Loan Price	3.00%	0.00%
Other Debt \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Loan Price	84.00%	75.00%
Other Debt \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)	11.00%	15.00%
Comparable Loan Price	65.00%	39.00%
Other Debt \| Margin Loan Model \| Minimum
Fair Value Inputs
Discount Rate	1.00%
Other Debt \| Margin Loan Model \| Maximum
Fair Value Inputs
Discount Rate	2.00%
Other Debt \| Margin Loan Model \| Weighted Average
Fair Value Inputs
Discount Rate	1.00%
Other Debt \| Option Model \| Minimum
Fair Value Inputs
At the Money Volatility	16.00%	15.00%
Other Debt \| Option Model \| Maximum
Fair Value Inputs
At the Money Volatility	53.00%	54.00%
Other Debt \| Option Model \| Weighted Average
Fair Value Inputs
At the Money Volatility	16.00%	15.00%
Corporate Equities
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 575	$ 272
Liabilities	$ 97
Corporate Equities \| Comparable Pricing
Fair Value Inputs
Comparable Equity Price	100.00%	100.00%
Corporate Equities \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Equity Price (Liabilities)	0.00%
Comparable Price	59.00%	83.00%
Corporate Equities \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Equity Price (Liabilities)	100.00%
Comparable Price	91.00%	96.00%
Corporate Equities \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Equity Price	100.00%	100.00%
Comparable Equity Price (Liabilities)	80.00%
Comparable Price	78.00%	85.00%
Corporate Equities \| Net Asset Value \| Minimum
Fair Value Inputs
Discount to Net Asset Value		0.00%
Corporate Equities \| Net Asset Value \| Maximum
Fair Value Inputs
Discount to Net Asset Value		71.00%
Corporate Equities \| Net Asset Value \| Weighted Average
Fair Value Inputs
Discount to Net Asset Value		36.00%
Corporate Equities \| Market Approach
Fair Value Inputs
EBITDA Multiple	9
Price/Book ratio	0	0
Corporate Equities \| Market Approach \| Minimum
Fair Value Inputs
EBITDA Multiple		6
Corporate Equities \| Market Approach \| Maximum
Fair Value Inputs
EBITDA Multiple		9
Corporate Equities \| Market Approach \| Weighted Average
Fair Value Inputs
EBITDA Multiple	9	8
Price/Book ratio	0	0
Interest Rate Contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 89	$ (173)
Interest Rate Contracts \| Option Model
Fair Value Inputs
Inflation Volatility	60.00%
Interest Rate Contracts \| Option Model \| Minimum
Fair Value Inputs
Interest Rate Volatility Concentration Liquidity Multiple	0	0
Interest Rate Volatility Skew	32.00%	38.00%
Interest Rate Quanto Correlation	(8.00%)	(9.00%)
Interest Rate - Foreign Exchange Correlation	26.00%	28.00%
Interest Rate - Inflation Correlation	(43.00%)	(44.00%)
Inflation Volatility		69.00%
Interest Rate Curve Correlation	24.00%	44.00%
Interest Rate Contracts \| Option Model \| Maximum
Fair Value Inputs
Interest Rate Volatility Concentration Liquidity Multiple	3	3
Interest Rate Volatility Skew	91.00%	104.00%
Interest Rate Quanto Correlation	37.00%	35.00%
Interest Rate - Foreign Exchange Correlation	62.00%	62.00%
Interest Rate - Inflation Correlation	(41.00%)	(40.00%)
Inflation Volatility		71.00%
Interest Rate Curve Correlation	93.00%	87.00%
Interest Rate Contracts \| Option Model \| Weighted Average
Fair Value Inputs
Interest Rate Volatility Concentration Liquidity Multiple	2	2
Interest Rate Contracts \| Option Model \| Simple Average
Fair Value Inputs
Interest Rate Volatility Skew	44.00%	86.00%
Interest Rate Quanto Correlation	2.00%	6.00%
Interest Rate - Foreign Exchange Correlation	44.00%	44.00%
Interest Rate - Inflation Correlation	(43.00%)	(42.00%)
Inflation Volatility	60.00%	70.00%
Interest Rate Curve Correlation	69.00%	73.00%
Interest Rate Contracts \| Option Model \| Median
Fair Value Inputs
Interest Rate Volatility Skew	43.00%	60.00%
Interest Rate Quanto Correlation	(8.00%)	(6.00%)
Interest Rate - Foreign Exchange Correlation	43.00%	42.00%
Interest Rate - Inflation Correlation	(43.00%)	(43.00%)
Inflation Volatility	60.00%	71.00%
Interest Rate Curve Correlation	75.00%	80.00%
Credit Contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ (805)	$ (743)
Credit Contracts \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - lower (higher)	0.00%	0.00%
Cash Synthetic Basis	5.00%	5.00%
Credit Contracts \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - lower (higher)	75.00%	55.00%
Cash Synthetic Basis	12.00%	13.00%
Credit Contracts \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - lower (higher)	25.00%	18.00%
Cash Synthetic Basis	9.00%	9.00%
Credit Contracts \| Correlation Model \| Minimum
Fair Value Inputs
Credit Correlation	34.00%	42.00%
Credit Contracts \| Correlation Model \| Maximum
Fair Value Inputs
Credit Correlation	99.00%	95.00%
Credit Contracts \| Correlation Model \| Weighted Average
Fair Value Inputs
Credit Correlation	58.00%	63.00%
Foreign Exchange Contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 66	$ 151
Foreign Exchange Contracts \| Option Model \| Minimum
Fair Value Inputs
Interest Rate Volatility Skew	32.00%
Interest rate curve	0.00%	0.00%
Interest Rate Quanto Correlation	(8.00%)	(9.00%)
Interest Rate - Credit Spread Correlation		(54.00%)
Interest Rate - Foreign Exchange Correlation	26.00%	28.00%
Interest Rate Curve Correlation		44.00%
Foreign Exchange Contracts \| Option Model \| Maximum
Fair Value Inputs
Interest Rate Volatility Skew	91.00%
Interest rate curve	1.00%	2.00%
Interest Rate Quanto Correlation	37.00%	35.00%
Interest Rate - Credit Spread Correlation		(2.00%)
Interest Rate - Foreign Exchange Correlation	62.00%	62.00%
Interest Rate Curve Correlation		87.00%
Foreign Exchange Contracts \| Option Model \| Simple Average
Fair Value Inputs
Interest Rate Volatility Skew	44.00%
Interest rate curve	0.00%	1.00%
Interest Rate Quanto Correlation	2.00%	6.00%
Interest Rate - Credit Spread Correlation		(17.00%)
Interest Rate - Foreign Exchange Correlation	44.00%	44.00%
Interest Rate Curve Correlation		73.00%
Foreign Exchange Contracts \| Option Model \| Median
Fair Value Inputs
Interest Rate Volatility Skew	43.00%
Interest rate curve	0.00%	1.00%
Interest Rate Quanto Correlation	(8.00%)	(6.00%)
Interest Rate - Credit Spread Correlation		(11.00%)
Interest Rate - Foreign Exchange Correlation	43.00%	42.00%
Interest Rate Curve Correlation		80.00%
Equity Contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ (2,041)	$ (2,165)
Liabilities derivative equity contract increased by		$ 785
Equity Contracts \| Option Model \| Minimum
Fair Value Inputs
At the Money Volatility	16.00%	14.00%
Volatility Skew	(3.00%)	(2.00%)
Equity - Equity Correlation	40.00%	40.00%
Equity - Foreign Exchange Correlation	(50.00%)	(50.00%)
Equity - Interest Rate Correlation	(31.00%)	(18.00%)
Equity Contracts \| Option Model \| Maximum
Fair Value Inputs
At the Money Volatility	62.00%	51.00%
Volatility Skew	0.00%	0.00%
Equity - Equity Correlation	99.00%	99.00%
Equity - Foreign Exchange Correlation	10.00%	10.00%
Equity - Interest Rate Correlation	50.00%	81.00%
Equity Contracts \| Option Model \| Weighted Average
Fair Value Inputs
At the Money Volatility	31.00%	29.00%
Volatility Skew	(1.00%)	(1.00%)
Equity - Equity Correlation	72.00%	72.00%
Equity - Foreign Exchange Correlation	(16.00%)	(16.00%)
Equity Contracts \| Option Model \| Simple Average
Fair Value Inputs
Equity - Interest Rate Correlation	14.00%	26.00%
Equity Contracts \| Option Model \| Median
Fair Value Inputs
Equity - Interest Rate Correlation	7.00%	11.00%
Commodity Contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 1,432	$ 1,146
Commodity Contracts \| Option Model \| Minimum
Fair Value Inputs
Forward Power Price (per megawatt hour) \| $ / MWh	4	5
Commodity Volatility	10.00%	11.00%
Cross Commodity Correlation	43.00%	33.00%
Commodity Contracts \| Option Model \| Maximum
Fair Value Inputs
Forward Power Price (per megawatt hour) \| $ / MWh	91	106
Commodity Volatility	59.00%	90.00%
Cross Commodity Correlation	100.00%	100.00%
Commodity Contracts \| Option Model \| Weighted Average
Fair Value Inputs
Forward Power Price (per megawatt hour) \| $ / MWh	33	38
Commodity Volatility	18.00%	19.00%
Cross Commodity Correlation	93.00%	93.00%
Principal Investments
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 541	$ 835
Principal Investments \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Equity Price	75.00%	64.00%
Principal Investments \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Equity Price	100.00%	100.00%
Principal Investments \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Equity Price	84.00%	95.00%
Principal Investments \| Discounted Cash Flow
Fair Value Inputs
Implied Weighted Average Cost of Capital	14.00%	11.00%
Exit Multiple	10	10
Equity Discount Rate		25.00%
Principal Investments \| Discounted Cash Flow \| Minimum
Fair Value Inputs
Capitalization Rate	5.00%
Equity Discount Rate	18.00%
Principal Investments \| Discounted Cash Flow \| Maximum
Fair Value Inputs
Capitalization Rate	10.00%
Equity Discount Rate	35.00%
Principal Investments \| Discounted Cash Flow \| Weighted Average
Fair Value Inputs
Implied Weighted Average Cost of Capital	14.00%	11.00%
Exit Multiple	10	10
Capitalization Rate	6.00%
Equity Discount Rate	21.00%	25.00%
Principal Investments \| Market Approach
Fair Value Inputs
Price / Earnings ratio		23
Principal Investments \| Market Approach \| Minimum
Fair Value Inputs
EBITDA Multiple	9	4
Forward capacity price (per capacity power unit) \| $ / PowerCapacityUnit	5	5
Principal Investments \| Market Approach \| Maximum
Fair Value Inputs
EBITDA Multiple	19	14
Forward capacity price (per capacity power unit) \| $ / PowerCapacityUnit	9	7
Principal Investments \| Market Approach \| Weighted Average
Fair Value Inputs
EBITDA Multiple	11	10
Price / Earnings ratio		23
Forward capacity price (per capacity power unit) \| $ / PowerCapacityUnit	7	7
Other Investments
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Assets	$ 312	$ 323
Other Investments \| Comparable Pricing
Fair Value Inputs
Comparable Equity Price	100.00%	100.00%
Other Investments \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Equity Price	100.00%	100.00%
Other Investments \| Discounted Cash Flow
Fair Value Inputs
Implied Weighted Average Cost of Capital	10.00%
Exit Multiple	10
Other Investments \| Discounted Cash Flow \| Minimum
Fair Value Inputs
Implied Weighted Average Cost of Capital		10.00%
Exit Multiple		6
Other Investments \| Discounted Cash Flow \| Maximum
Fair Value Inputs
Implied Weighted Average Cost of Capital		13.00%
Exit Multiple		9
Other Investments \| Discounted Cash Flow \| Weighted Average
Fair Value Inputs
Implied Weighted Average Cost of Capital	10.00%	11.00%
Exit Multiple	10	9
Other Investments \| Market Approach \| Minimum
Fair Value Inputs
EBITDA Multiple	8	9
Other Investments \| Market Approach \| Maximum
Fair Value Inputs
EBITDA Multiple	14	13
Other Investments \| Market Approach \| Weighted Average
Fair Value Inputs
EBITDA Multiple	10	10
Short-term Borrowings \| Comparable Pricing
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Liabilities	$ 69
Fair Value Inputs
Comparable Equity Price	20.00%
Short-term Borrowings \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Equity Price	20.00%
Securities Sold under Agreements to Repurchase
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Liabilities	$ 154	$ 153
Securities Sold under Agreements to Repurchase \| Discounted Cash Flow \| Minimum
Fair Value Inputs
Funding Spread	0.96%	0.75%
Securities Sold under Agreements to Repurchase \| Discounted Cash Flow \| Maximum
Fair Value Inputs
Funding Spread	1.23%	0.91%
Securities Sold under Agreements to Repurchase \| Discounted Cash Flow \| Weighted Average
Fair Value Inputs
Funding Spread	1.13%	0.86%
Other Secured Financings
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Liabilities	$ 341	$ 149
Other Secured Financings \| Comparable Pricing
Fair Value Inputs
Comparable Bond Price - higher (lower)	100.00%
Other Secured Financings \| Comparable Pricing \| Minimum
Fair Value Inputs
Comparable Bond Price - higher (lower)		99.00%
Other Secured Financings \| Comparable Pricing \| Maximum
Fair Value Inputs
Comparable Bond Price - higher (lower)		101.00%
Other Secured Financings \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Bond Price - higher (lower)	100.00%	100.00%
Other Secured Financings \| Discounted Cash Flow \| Minimum
Fair Value Inputs
Discount Rate	4.00%
Funding Spread	1.08%	0.82%
Other Secured Financings \| Discounted Cash Flow \| Maximum
Fair Value Inputs
Discount Rate	17.00%
Funding Spread	1.30%	0.98%
Other Secured Financings \| Discounted Cash Flow \| Weighted Average
Fair Value Inputs
Discount Rate	5.00%
Funding Spread	1.19%	0.95%
Long-term Borrowings
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Liabilities	$ 2,462	$ 1,934
Long-term Borrowings \| Comparable Pricing
Fair Value Inputs
Comparable Equity Price (Liabilities)	100.00%
Long-term Borrowings \| Comparable Pricing \| Weighted Average
Fair Value Inputs
Comparable Equity Price (Liabilities)	100.00%
Long-term Borrowings \| Correlation Model \| Minimum
Fair Value Inputs
Credit Correlation	40.00%	48.00%

Fair Value Disclosures (Quantitative Information about and Sensitivity of Significant Unobservable Inputs Used in Recurring Level 3 Fair Value Measurements) (Details) - Recurring - Level 3
$ in Millions