Investments (details) - Mortgage-Backed Securities and CMOs (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investment disclosure details
Fixed maturities, available for sale, at fair value	$ 65,393	$ 64,232
Residential mortgage-backed pass-through securities classified as available-for-sale, GNMA, FNMA, FHLMC [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	1,440	1,820
Residential collateralized mortgage obligations [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	1,560	1,700
Percent guaranteed by or fully collateralized by securities issued by GNMA, FNMA or FHLMC	43.00%	38.00%
Non-guaranteed residential collateralized mortgage obligations [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	893	1,050
Commercial mortgage-backed securities [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	453	446
Commercial mortgage-backed securities, containing guarantees by the U.S. government or a government-sponsored enterprise [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	64	81
Commercial mortgage-backed securities, Canadian non-guaranteed securities [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	4	10
Commercial mortgage-backed securities, non-guaranteed securities [Member]
Investment disclosure details
Fixed maturities, available for sale, at fair value	$ 389	$ 365
Percent of non-guaranteed securities issued in 2004 and prior years	51.00%	71.00%

Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

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