Change in AOCI Includes Changes in Unrealized Gains and Losses on Investments and Pension Obligations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated unrealized gains on investments available for sale and other at beginning of period	$ 1,232	$ 1,012	$ 570
Increase in unrealized gains	309	387	936
Cumulative effect of change in accounting for other-than-temporary impairments	0	0	(163)
Reclassification adjustment for (gains) losses included in net income	(70)	(159)	(336)
Adjustment to deferred acquisition costs and life policy reserves and other	(11)	(8)	5
Effect on other comprehensive income	228	220	442
Accumulated unrealized gains on investments available for sale and other at end of period	1,460	1,232	1,012
Accumulated unrealized losses for pension obligations at beginning of period	(63)	(66)	(52)
Change in pension obligations	(25)	3	(14)
Accumulated unrealized losses for pension obligations at end of period	(88)	(63)	(66)
Accumulated other comprehensive income before tax
Accumulated other comprehensive income at beginning of period	1,169	946	518
Unrealized investment gains and losses and other adjustments	228	220	442
Change in pension obligations	(25)	3	(14)
Accumulated other comprehensive income at end of period	1,372	1,169	946
Accumulated unrealized gains on investments available for sale and other at beginning of period	422	345	189
Increase in unrealized gains	108	136	330
Cumulative effect of change in accounting for other-than-temporary impairments	0	0	(57)
Reclassification adjustment for (gains) losses included in net income	(25)	(56)	(119)
Adjustment to deferred acquisition costs and life policy reserves and other	(3)	(3)	2
Effect on other comprehensive income	80	77	156
Accumulated unrealized gains on investments available for sale and other at end of period	502	422	345
Accumulated unrealized losses for pension obligations at beginning of period	(22)	(23)	(18)
Change in pension obligations	(9)	1	(5)
Accumulated unrealized losses for pension obligations at end of period	(31)	(22)	(23)
Accumulated other comprehensive income, tax
Accumulated other comprehensive income at beginning of period	400	322	171
Unrealized investment gains and losses and other adjustments	80	77	156
Change in pension obligations	(9)	1	(5)
Accumulated other comprehensive income at end of period	471	400	322
Accumulated unrealized gains on investments available for sale and other at beginning of period	810	667	381
Increase in unrealized gains	201	251	606
Cumulative effect of change in accounting for other-than-temporary impairments	0	0	(106)
Reclassification adjustment for (gains) losses included in net income	(45)	(103)	(217)
Adjustment to deferred acquisition costs and life policy reserves and other	(8)	(5)	3
Effect on other comprehensive income	148	143	286
Accumulated unrealized gains on investments available for sale and other at end of period	958	810	667
Accumulated unrealized losses for pension obligations at beginning of period	(41)	(43)	(34)
Change in pension obligations	(16)	2	(9)
Accumulated unrealized losses for pension obligations at end of period	(57)	(41)	(43)
Accumulated other comprehensive income net of tax
Accumulated other comprehensive income at beginning of period	769	624	347
Unrealized investment gains and losses and other adjustments	148	143	286
Change in pension obligations	(16)	2	(9)
Accumulated other comprehensive income at end of period	$ 901	$ 769	$ 624