Income Taxes - Affordable Housing Tax Credits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Tax credit and other tax benefits	$ 1,600	$ 1,600	$ 1,500
Amount of amortization reported in income tax expense	1,100	1,100	$ 989
Carrying value of investments, reported in other assets	7,700	7,300
Amount of commitments, reported in account payable and other liabilities	$ 2,000	$ 1,800