Investments (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Investment [Line Items]
Reduction in net unrealized gains on investments in AOCI supporting certain insurance products, net of tax and noncontrolling interests			$ 1,100.0		$ 651.0
Pretax net unrealized gains (losses) on available-for-sale securities reclassified out of AOCI into earnings	12	(29)	59	12
Future capital call commitments	114		114
Commitments to purchase various privately placed debt securities, including bank loans	159		159
Commitments to sell various privately placed debt securities, including bank loans	154		154
Unfunded bank loan participations	$ 6		$ 6