Investments (Amortized Cost and Fair Value of Fixed Maturities by Contractual Maturities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Available for Sale Amortized Cost
Due in one year or less	$ 8,173
Due after one year through five years	47,775
Due after five years through ten years	55,112
Due after ten years	96,095
Debt Maturities, without single maturity date	33,269
Total	240,424		187,754
Available for Sale Securities Fair Value
Due in one year or less	8,192
Due after one year through five years	48,372
Due after five years through ten years	58,167
Due after ten years	107,288
Debt Maturities, without Single Maturity Date	32,629
Total	254,648		194,983
Held to Maturity Securities Amortized Cost
Due in one year or less	0
Due after one year through five years	59
Due after five years through ten years	422
Due after ten years	1,936	[1]
Debt Maturities, without Single Maturity Date	2,690
Total	5,107		5,226
Held to Maturity Securities Fair Value
Due in one year or less	0
Due after one year through five years	60
Due after five years through ten years	427
Due after ten years	1,981	[1]
Debt Maturities, without Single Maturity Date	2,886
Total	5,354		5,477
Collateralized Securities [Member]
Available for Sale Amortized Cost
Total	240,424
Available for Sale Securities Fair Value
Total	254,648
Held to Maturity Securities Amortized Cost
Total	5,107
Held to Maturity Securities Fair Value
Total	5,354
Residential Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	9,404
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	9,856
Held to Maturity Securities Amortized Cost
Debt Maturities, without Single Maturity Date	1,049
Held to Maturity Securities Fair Value
Debt Maturities, without Single Maturity Date	1,114
Commercial Mortgage Backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	11,519
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	12,080
Held to Maturity Securities Amortized Cost
Debt Maturities, without Single Maturity Date	428
Held to Maturity Securities Fair Value
Debt Maturities, without Single Maturity Date	497
Asset-backed Securities [Member]
Available for Sale Amortized Cost
Debt Maturities, without single maturity date	12,346
Available for Sale Securities Fair Value
Debt Maturities, without Single Maturity Date	10,693
Held to Maturity Securities Amortized Cost
Debt Maturities, without Single Maturity Date	1,213
Held to Maturity Securities Fair Value
Debt Maturities, without Single Maturity Date	$ 1,275

[1] Excludes notes with amortized cost of $500 million (fair value, $519 million) which have been offset with the associated payables under a netting agreement.