Guarantees and Commitments Guarantees and Commitments (Contractual financing commitments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Guarantees [Abstract]
Commitment to provide capital to investees	$ 206	$ 132
Warehouse and construction lending commitments	164	197
Commitment to fund remaining unused balances on home equity lines of credit	356	358
Unused revolving credit line commitments and other	$ 1,995	$ 1,445