Correction of Prior Period Amounts (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other assets	$ 8,800	$ 8,496
Other liabilities	2,143	2,520
Retained earnings	10,936	10,101
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	18,355	17,386	$ 16,593
Noncontrolling interests	100	153
Noncontrolling Interests
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	100	153	215	$ 264
Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 10,936	$ 10,101	$ 9,116	$ 8,473