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Accounting Policies - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016 | Jan. 01, 2016
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Assets of managed investment entities | $ 4,873 |  | $ 4,873 |  | $ 4,765 |
Liabilities of managed investment entities | $ 4,685 |  | $ 4,685 |  | $ 4,549 |
Weighted average common shares adjustment related to stock-based compensation (shares) | 2,000,000 | 1,600,000 | 2,100,000 | 1,600,000 |  |
Anti-dilutive potential common shares related to stock-based compensation plans (shares) | 0 | 700,000 | 0 | 800,000 |  |
Maturities of short term investments |  |  | 3 months |  |  |
Retained Earnings | Maximum |  |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Cumulative effect of accounting change |  |  |  |  |  | $ 1

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