Invested Assets and Related Income (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Texas [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	$ 2,466
Amortized cost	2,269
Texas [Member] | Special Revenues Bond [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	1,035
Texas [Member] | Municipal and Political Subdivision General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	1,156
Texas [Member] | State General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	275
New York [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	1,560
Amortized cost	1,444
New York [Member] | Special Revenues Bond [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	1,385
New York [Member] | Municipal and Political Subdivision General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	139
New York [Member] | State General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	36
California [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	1,374
Amortized cost	1,278
California [Member] | Special Revenues Bond [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	994
California [Member] | Municipal and Political Subdivision General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	140
California [Member] | State General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	240
Illinois [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	1,177
Amortized cost	1,102
Illinois [Member] | Special Revenues Bond [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	617
Illinois [Member] | Municipal and Political Subdivision General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	486
Illinois [Member] | State General Obligation Bonds [Member]
Fair value and amortized cost for the tax exempt fixed maturities other than pre-refunded bonds for each state in which the Corporation's aggregate investment was 5% or more of total tax exempt fixed maturities [Abstract]
Fair value	$ 74