Summary of Significant Accounting Policies - Balance sheet (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assets	$ 245,192	$ 274,119
Liabilities	224,057	252,791
Retained earnings	16,049	14,737
Total equity	21,135	21,328
Total liabilities and equity	$ 245,192	274,119
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assets		274,119
Liabilities		252,646
Retained earnings		14,882
Total equity		21,473
Total liabilities and equity		274,119
Correction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Assets		0
Liabilities		145
Retained earnings		(145)
Total equity		(145)
Total liabilities and equity		$ 0