Fair Value Measurements (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Year	Dec. 31, 2011	Dec. 31, 2010
Fair Value Measurements Of Financial Instruments [Line Items]
GLB - Lapse rate - lower range	1.00%
GLB - Lapse rate - upper range	6.00%
GLB - Spike lapse rate - lower range	10.00%
GLB - Spike lapse rate - upper range	30.00%
GLB - Ultimate lapse rate	10.00%
GLB - Length of ultimate lapse rate period, years	2
GLB - Adjustment factor for valuable guarantees - lower	15.00%
GLB - Adjustment factor for valuable guarantees - upper	75.00%
Percent of GMIB guaranteed value that are represented by clients with several years of annuitization experience	36.00%
GLB - Maximum annuitization rate	8.00%
GLB - First year maximum annuitization rate	13.00%
GLB - Weighted average maximum annuitization rate - rate 1	8.00%
GLB - Weighted average maximum annuitization rate - rate 2	12.00%
GLB - Weighted average maximum annuitization rate - rate 3	30.00%
Guaranteed Living Benefits, Net Income Impact From Model Refinement	$ 49	$ 14	$ 98
Amounts of transfer from Level 1 to Level 2	40
Amounts of transfer from Level 2 to Level 1	15
Amounts included in Level 2 previosuly reported in Level 1	$ 417
Redemption Notice Periods Lower Range [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Notice period for redemption for alternative investments investment funds, days	5 days
Redemption Notice Periods Upper Range [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Notice period for redemption for alternative investments investment funds, days	120 days