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Fair Value Measurements (Narrative) (Detail) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) Year | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
GLB - Lapse rate - lower range |  | 3.00% |  |  |
GLB - Lapse rate - upper range |  | 9.00% |  |  |
GLB - Spike lapse rate - lower range |  | 6.00% |  |  |
GLB - Spike lapse rate - upper range |  | 33.00% |  |  |
GLB - Ultimate lapse rate |  | 10.00% |  |  |
GLB - Length of ultimate lapse rate period, years | Year |  | 2 |  |  |
GLB - Adjustment factor for valuable guarantees - lower |  | 15.00% |  |  |
GLB - Adjustment factor for valuable guarantees - upper |  | 75.00% |  |  |
Realized Gain Losses As A Result of Change in Partial Withdrawal Assumption |  | $ 43,000,000 |  |  |
Realized Gain Losses As A Result of Change in Lapse Assumption (GLB) |  | 9,000,000 |  |  |
Realized Gain Losses As A Result of Annuitization Changes (GLB) |  | 117,000,000 |  |  |
Realized Gain Losses As A Result of Valuation Model Refinement (GLB) |  | 94,000,000 |  |  |
Fair Value, Level 1 to Level 2 transfers, Amount |  | 0 | $ 0 | $ 0 |
Assets measured using NAV |  | 3,623,000,000 | 3,627,000,000 |  |
Other investments (cost – $4,417 and $4,270) |  | 4,672,000,000 | 4,519,000,000 |  |
Derivative, Gain (Loss) on Derivative, Net |  | 87,000,000 | (126,000,000) | (193,000,000) |
Guaranteed Minimum Income Benefit |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | [1] | 364,000,000 | 53,000,000 | (203,000,000) |
Guaranteed Minimum Income Benefit | Variable Annuity [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | [1] | $ 25,000,000 |  |  |
Minimum |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Notice period for redemption for alternative investments investment funds, days |  | 5 days |  |  |
Maximum |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Notice period for redemption for alternative investments investment funds, days |  | 120 days |  |  |
Other Investments [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Other investments (cost – $4,417 and $4,270) |  | $ 15,000,000 | 25,000,000 |  |
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Other investments (cost – $4,417 and $4,270) |  | 3,623,000,000 | 3,626,000,000 |  |
Guaranteed Minimum Income Benefit |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
GLB liability |  | $ 550,000,000 | $ 853,000,000 | $ 888,000,000 | $ 663,000,000
[1] | (2) Excludes foreign exchange gains (losses) related to GLB.

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