Variable Interest Entities - Summary of Assets and Liabilities Related to Consolidated Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Variable interest entities [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	$ 515	$ 707
Consolidated Liabilities	173	185
Asset-backed commercial paper conduits [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	116	250
Consolidated Liabilities	0	3
Low income housing limited liability partnership [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	399	457
Consolidated Liabilities	173	182
Interest bearing deposits with banks [Member] | Asset-backed commercial paper conduits [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	3	5
Held-to-maturity securities [Member] | Asset-backed commercial paper conduits [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	76	200
Other assets [Member] | Asset-backed commercial paper conduits [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	37	45
Other assets [Member] | Low income housing limited liability partnership [Member]
Variable Interest Entity [Line Items]
Consolidated Assets	399	457
Long-term debt [Member] | Low income housing limited liability partnership [Member]
Variable Interest Entity [Line Items]
Consolidated Liabilities	92	92
Other liabilities [Member] | Asset-backed commercial paper conduits [Member]
Variable Interest Entity [Line Items]
Consolidated Liabilities	0	3
Other liabilities [Member] | Low income housing limited liability partnership [Member]
Variable Interest Entity [Line Items]
Consolidated Liabilities	$ 81	$ 90