Recent Accounting Pronouncements (Narrative) (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
ASU 2016-01 [Member] | Financial Liabilities [Member]
Cumulative effect of prospective application of new accounting principle	$ 162
ASU 2016-01 [Member] | Equity Investments [Member]
Cumulative effect of prospective application of new accounting principle	2
ASU 2018-02 [Member]
Cumulative effect of prospective application of new accounting principle	$ 3