Schedule II - Condensed Financial Information, Credit Facility (Details) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013 Banks
Line of Credit Facility [Line Items]
Short-term and Long-term Debt Outstanding		$ 5,200,000,000
Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Initiation Date		Dec. 01, 2012
Line of Credit Facility, Expiration Date		Dec. 01, 2017
Line of Credit Facility, Term of Agreement	5 years
Line of Credit Facility, Maximum Borrowing Capacity	1,500,000,000
Line of Credit Facility, Number of Participating Banks		16
Line of Credit Facility, Optional Maximum Borrowing Capacity	2,000,000,000
Line of Credit Facility, Covenant Terms		This agreement has certain covenants, including a financial covenant requiring the Company to maintain a total debt-to-adjusted capital ratio at or below 0.50 to 1.00
Credit Facility Remaining Borrowing Capacity		6,000,000,000
Revolving Credit And Letter Of Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Maximum debt-to-adjusted capital ratio convenant	50.00%
Revolving Credit And Letter Of Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Maximum debt-to-adjusted capital ratio convenant	100.00%
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	500,000,000
Letters of Credit Outstanding, Amount		39,000,000
Primary Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Participating Banks		3
Line of Credit Facility, Collective Bank Percentage Committment		35.00%
Minor Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Participating Banks		13
Line of Credit Facility, Collective Bank Percentage Committment		65.00%
Parent Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Participating Banks		16
Line of Credit Facility, Optional Maximum Borrowing Capacity	2,000,000,000
Credit Facility Remaining Borrowing Capacity		6,000,000,000
Short-term and Long-term Debt Outstanding		5,200,000,000
Letters of Credit Outstanding, Amount		39,000,000
Parent Company [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Term of Agreement	5 years
Line of Credit Facility, Maximum Borrowing Capacity	1,500,000,000
Parent Company [Member] | Revolving Credit And Letter Of Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Maximum debt-to-adjusted capital ratio convenant	50.00%
Parent Company [Member] | Revolving Credit And Letter Of Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Maximum debt-to-adjusted capital ratio convenant	100.00%
Parent Company [Member] | Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 500,000,000
Parent Company [Member] | Primary Commitment Holders [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Participating Banks		3
Parent Company [Member] | Primary Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Collective Bank Percentage Committment		35.00%
Parent Company [Member] | Minor Commitment Holders [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Number of Participating Banks		13
Parent Company [Member] | Minor Commitment Holders [Member] | Revolving Credit And Letter Of Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Collective Bank Percentage Committment		65.00%