Investments (details) - OTTI Rollforward (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of year	$ 152	$ 135
Additions for OTTI securities where no credit losses were previously recognized		1
Additions for OTTI securities where credit losses have been previously recognized	3	3
Reductions due to sales/defaults of credit-impaired securities		(1)
Adjustments to book value of credit-impaired securities due to changes in cash flows	1	1
Cumulative OTTI credit losses recognized for securities still held, end of period	156	139
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of year	58	47
Additions for OTTI securities where credit losses have been previously recognized	1	2
Cumulative OTTI credit losses recognized for securities still held, end of period	59	49
All other corporate bonds [Member]
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of year	94	88
Additions for OTTI securities where no credit losses were previously recognized		1
Additions for OTTI securities where credit losses have been previously recognized	2	1
Reductions due to sales/defaults of credit-impaired securities		(1)
Adjustments to book value of credit-impaired securities due to changes in cash flows	1	1
Cumulative OTTI credit losses recognized for securities still held, end of period	$ 97	$ 90