Investments (Detail - Credit risk profile) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	$ 2,851	$ 3,301
Loan To Value Ratio Below 50 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	355	342
Loan To Value Ratio 50 Percent To 59 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	795	570
Loan To Value Ratio 60 Percent To 69 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	703	905
Loan To Value Ratio 70 Percent To 79 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	489	561
Loan To Value Ratio 80 Percent To 89 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	294	402
Loan To Value Ratio 90 Percent To 99 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	102	275
Loan To Value Ratio 100 Percent Or Above [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	113	246
Debt Service Coverage Ratio 1.30x Or Greater [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	1,726	1,567
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio Below 50 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	297	225
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio 50 Percent To 59 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	614	444
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio 60 Percent To 69 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	562	646
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio 70 Percent To 79 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	194	117
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio 80 Percent To 89 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	45	99
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio 90 Percent To 99 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	14	36
Debt Service Coverage Ratio 1.30x Or Greater [Member] | Loan To Value Ratio 100 Percent Or Above [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	0
Debt Service Coverage Ratio 1.20x To 1.29x [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	402	500
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio Below 50 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	8	55
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio 50 Percent To 59 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	104	47
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio 60 Percent To 69 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	75	140
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio 70 Percent To 79 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	143	132
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio 80 Percent To 89 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	42	81
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio 90 Percent To 99 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	30	35
Debt Service Coverage Ratio 1.20x To 1.29x [Member] | Loan To Value Ratio 100 Percent Or Above [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	10
Debt Service Coverage Ratio 1.10x To 1.19x [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	318	350
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio Below 50 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	3
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio 50 Percent To 59 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	25	26
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio 60 Percent To 69 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	42
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio 70 Percent To 79 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	132	120
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio 80 Percent To 89 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	131	79
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio 90 Percent To 99 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	30
Debt Service Coverage Ratio 1.10x To 1.19x [Member] | Loan To Value Ratio 100 Percent Or Above [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	30	50
Debt Service Coverage Ratio 1.00x To 1.09x [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	207	390
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio Below 50 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	50	50
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio 50 Percent To 59 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	52	0
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio 60 Percent To 69 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	66	0
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio 70 Percent To 79 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	4	159
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio 80 Percent To 89 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	18	72
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio 90 Percent To 99 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	58
Debt Service Coverage Ratio 1.00x To 1.09x [Member] | Loan To Value Ratio 100 Percent Or Above [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	17	51
Debt Service Coverage Ratio Less Than 1.00x [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	198	494
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio Below 50 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	9
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio 50 Percent To 59 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	53
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio 60 Percent To 69 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	0	77
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio 70 Percent To 79 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	16	33
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio 80 Percent To 89 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	58	71
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio 90 Percent To 99 Percent [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	58	116
Debt Service Coverage Ratio Less Than 1.00x [Member] | Loan To Value Ratio 100 Percent Or Above [Member]
Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Line Items]
Commercial mortgage loan	$ 66	$ 135