Fair Value Measurements - Quantative Information about Level 3 Fair Value (Details)	3 Months Ended
	Jun. 30, 2014
Discounted Cash Flow | Illiquidity Premium | Auction rate securities
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	3.00%
Discounted Cash Flow | Counterparty Credit Spread | Auction rate securities
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	1.00%
Fair Value Measurement Range, Maximum	3.00%
Discounted Cash Flow | Time To Principal Recovery | Auction rate securities
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range Min, Term	8 years
Year Four [Member] | Option Model | Implied Volatility | Fuel derivatives
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	11.00%
Fair Value Measurement Range, Maximum	14.00%
Third Quarter of 2014 | Option Model | Implied Volatility | Fuel derivatives
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	8.00%
Fair Value Measurement Range, Maximum	19.00%
Fourth Quarter of 2014 | Option Model | Implied Volatility | Fuel derivatives
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	12.00%
Fair Value Measurement Range, Maximum	19.00%
2015 | Option Model | Implied Volatility | Fuel derivatives
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	12.00%
Fair Value Measurement Range, Maximum	20.00%
2016 | Option Model | Implied Volatility | Fuel derivatives
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	11.00%
Fair Value Measurement Range, Maximum	19.00%
2017 | Option Model | Implied Volatility | Fuel derivatives
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	11.00%
Fair Value Measurement Range, Maximum	16.00%