Variable Interest Entities Reflects adoption of ASU 2015-12 - Schedule of Net Gain (Loss) Related to Consolidated VIEs (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Variable Interest Entity [Line Items]
Nonoperating net gain (loss) on consolidated VIEs	$ 15	$ 51
Net income (loss) attributable to noncontrolling interests	5	9
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Nonoperating net gain (loss) on consolidated VIEs	2	33
Net income (loss) attributable to noncontrolling interests	$ 5	$ 8

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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