Fair Value (Carrying amount and estimated fair value of financial instrument assets and liabilities which are not measured at fair value) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financial Assets [Abstract]
Notes receivable for the issuance of common stock	$ 21	$ 22
Mortgage loans	401	234
Financial Liabilities [Abstract]
Short term debt	13	83
Long term debt	2,557	2,525
Carrying Amount [Member]
Financial Assets [Abstract]
Notes receivable for the issuance of common stock	21	22
Mortgage loans	401	234
Financial Liabilities [Abstract]
Premium deposits and annuity contracts	100	109
Short term debt	13	83
Long term debt	2,557	2,525
Estimated Fair Value [Member]
Financial Assets [Abstract]
Notes receivable for the issuance of common stock	21	22
Mortgage loans	418	247
Financial Liabilities [Abstract]
Premium deposits and annuity contracts	104	114
Short term debt	13	84
Long term debt	3,016	2,679
Level 1 [Member] | Estimated Fair Value [Member]
Financial Assets [Abstract]
Notes receivable for the issuance of common stock
Mortgage loans
Financial Liabilities [Abstract]
Premium deposits and annuity contracts
Short term debt
Long term debt
Level 2 [Member] | Estimated Fair Value [Member]
Financial Assets [Abstract]
Notes receivable for the issuance of common stock
Mortgage loans
Financial Liabilities [Abstract]
Premium deposits and annuity contracts
Short term debt	13
Long term debt	3,016
Level 3 [Member] | Estimated Fair Value [Member]
Financial Assets [Abstract]
Notes receivable for the issuance of common stock	21
Mortgage loans	418
Financial Liabilities [Abstract]
Premium deposits and annuity contracts	104
Short term debt
Long term debt