Investments (details) - OTTI Rollforward (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
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	$ 165	$ 152
Additions for OTTI securities where credit losses have been previously recognized	1	3
Adjustments to book value of credit-impaired securities due to changes in cash flows	2	1
Cumulative OTTI credit losses recognized for securities still held, end of period	168	156
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	63	58
Additions for OTTI securities where credit losses have been previously recognized	1	1
Adjustments to book value of credit-impaired securities due to changes in cash flows	1
Cumulative OTTI credit losses recognized for securities still held, end of period	65	59
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	102	94
Additions for OTTI securities where credit losses have been previously recognized		2
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	$ 103	$ 97