Fair Value Measurements (Non-Recurring Measurement) (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Measurements, Recurring [Member] | Domestic Corporate Debt Securities [Member] | Income Approach Valuation Techniques [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 1,585	$ 1,652
Weighted Average Discount Rate Used For Level Three Valuation	11.30%	11.10%
Fair Value, Measurements, Recurring [Member] | Domestic Corporate Debt Securities [Member] | Income Approach Valuation Techniques [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Discount Rate Used For Level Three Valuation	1.80%	1.30%
Fair Value, Measurements, Recurring [Member] | Domestic Corporate Debt Securities [Member] | Income Approach Valuation Techniques [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Discount Rate Used For Level Three Valuation	38.00%	29.90%
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member] | Income Approach Valuation Techniques [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	4,869	4,977
Weighted Average Discount Rate Used For Level Three Valuation	3.60%	3.80%
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member] | Income Approach Valuation Techniques [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Discount Rate Used For Level Three Valuation	1.70%	2.10%
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member] | Income Approach Valuation Techniques [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Discount Rate Used For Level Three Valuation	13.10%	13.10%
Fair Value, Measurements, Recurring [Member] | Foreign Corporate Debt Securities [Member] | Income Approach Valuation Techniques [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	1,016	865
Weighted Average Discount Rate Used For Level Three Valuation	11.80%	13.20%
Fair Value, Measurements, Recurring [Member] | Foreign Corporate Debt Securities [Member] | Income Approach Valuation Techniques [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Discount Rate Used For Level Three Valuation	2.30%	1.50%
Fair Value, Measurements, Recurring [Member] | Foreign Corporate Debt Securities [Member] | Income Approach Valuation Techniques [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Discount Rate Used For Level Three Valuation	23.90%	25.00%
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Income Approach Valuation Techniques [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	358	360
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Income Approach Valuation Techniques [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Cost Of Capital Used For Level Three Valuation	8.10%
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Income Approach Valuation Techniques [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Cost Of Capital Used For Level Three Valuation	9.40%
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Cost Of Capital Used For Level Three Valuation		8.70%
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Cost Of Capital Used For Level Three Valuation		8.70%
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Cost Of Capital Used For Level Three Valuation		10.20%
Fair Value, Measurements, Recurring [Member] | Other 1 [Member] | Market Comparables Valuation Technique [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Cost Of Capital Used For Level Three Valuation	8.80%
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Income Approach Valuation Techniques [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Capitalization Rate Used For Level Three Valuation	8.00%	8.00%
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Income Approach Valuation Techniques [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation	5.40%	3.80%
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Income Approach Valuation Techniques [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation	13.70%	14.00%
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	1,513	2,633
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Business Enterprise Value Valuation Technique [Member] | EBITDA Multiple [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	106	202
Weighted Average EBITDA Multiple Used For Level Three Valuation		4.8
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Business Enterprise Value Valuation Technique [Member] | EBITDA Multiple [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range EBITDA Multiple Used For Level Three Valuation	4.3	2.0
Fair Value, Measurements, Nonrecurring [Member] | Financing receivables and loans held for sale [Member] | Business Enterprise Value Valuation Technique [Member] | EBITDA Multiple [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range EBITDA Multiple Used For Level Three Valuation	7.0	6.0
Weighted Average EBITDA Multiple Used For Level Three Valuation	5.7
Fair Value, Measurements, Nonrecurring [Member] | Cost and equity method investments [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	38	72
Weighted Average Capitalization Rate Used For Level Three Valuation	10.30%	12.00%
Fair Value, Measurements, Nonrecurring [Member] | Cost and equity method investments [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation	7.70%	9.20%
Fair Value, Measurements, Nonrecurring [Member] | Cost and equity method investments [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation	10.60%	12.80%
Fair Value, Measurements, Nonrecurring [Member] | Long Lived Assets, Including Real Estate [Member] | Income Approach Valuation Techniques [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Weighted Average Capitalization Rate Used For Level Three Valuation		7.30%
Fair Value, Measurements, Nonrecurring [Member] | Long Lived Assets, Including Real Estate [Member] | Income Approach Valuation Techniques [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation		4.80%
Fair Value, Measurements, Nonrecurring [Member] | Long Lived Assets, Including Real Estate [Member] | Income Approach Valuation Techniques [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation		14.60%
Fair Value, Measurements, Nonrecurring [Member] | Long Lived Assets, Including Real Estate [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Investments, Fair Value Disclosure	$ 1,078	$ 985
Weighted Average Capitalization Rate Used For Level Three Valuation	7.80%
Fair Value, Measurements, Nonrecurring [Member] | Long Lived Assets, Including Real Estate [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member] | Lower Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation	7.70%
Fair Value, Measurements, Nonrecurring [Member] | Long Lived Assets, Including Real Estate [Member] | Income Approach Valuation Techniques [Member] | Capitalization Rate Unobservable Inputs [Member] | Upper Limit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Range Capitalization Rate Used For Level Three Valuation	14.50%