Fair Value Measurements (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012	Dec. 31, 2011
Financial assets:
Cash and cash equivalents	$ 1,529		$ 1,705		$ 1,422	$ 1,324
Mortgage loans	584		607
Policy loans	224		228
Financial liabilities:
Long-term debt	950		953
Level 1 [Member]
Financial assets:
Cash and cash equivalents	1,529		1,705
Total financial assets not accounted for at fair value	1,529		1,705
Level 2 [Member]
Financial liabilities:
Long-term debt	1,014		990
Total financial liabilities not accounted for at fair value	1,014		990
Level 3 [Member]
Financial assets:
Mortgage loans	590		613
Policy loans	224		228
Total financial assets not accounted for at fair value	814		841
Financial liabilities:
Annuity benefits accumulated	17,700	[1]	17,422	[1]
Long-term debt	93		96
Total financial liabilities not accounted for at fair value	17,793		17,518
Carrying Value [Member]
Financial assets:
Cash and cash equivalents	1,529		1,705
Mortgage loans	584		607
Policy loans	224		228
Total financial assets not accounted for at fair value	2,337		2,540
Financial liabilities:
Annuity benefits accumulated	17,872	[1]	17,405	[1]
Long-term debt	950		953
Total financial liabilities not accounted for at fair value	18,822		18,358
Fair Value [Member]
Financial assets:
Cash and cash equivalents	1,529		1,705
Mortgage loans	590		613
Policy loans	224		228
Total financial assets not accounted for at fair value	2,343		2,546
Financial liabilities:
Annuity benefits accumulated	17,700	[1]	17,422	[1]
Long-term debt	1,107		1,086
Total financial liabilities not accounted for at fair value	$ 18,807		$ 18,508

[1] Excludes life contingent annuities in the payout phase.