Asset Quality - Credit Risk Profile Based on Payment Activity (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	$ 62,098	$ 59,876	$ 58,264
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	15,271	15,604	15,841
Credit Risk Profile [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	2,924	3,027	3,057
Performing [Member] | Credit Risk Profile [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	2,918	3,017	3,045
Nonperforming [Member] | Credit Risk Profile [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	6	10	12
Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,584	1,600	1,595
Consumer Direct Loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1,583	1,598	1,594
Consumer Direct Loans [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	1	2	1
Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	813	806	753
Consumer Credit Card Financing Receivable [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	811	804	751
Consumer Credit Card Financing Receivable [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	2	2	2
Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	527	621	709
Consumer Indirect Loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	524	615	700
Consumer Indirect Loans [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit risk profile based on payment	$ 3	$ 6	$ 9