Income Taxes (Income Taxes - Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Taxes
Applicable income tax expense	$ 475	$ 178	$ 694	$ 390	[1]
Effective tax rate	31.90%	25.60%	29.20%	25.00%
Net tax deficiency reclassified from capital surplus to applicable income tax expense				$ 6

[1] Net tax deficiencies of $ 6 were reclassified from capital surplus to applicable income tax expense for the nine months ended September 30, 2016 , related to the early adoption of ASU 2016-09 during the fourth quarter of 2016, with an effective date of January 1, 2016