Guarantees and Commitments (Contractual Financing Commitments) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Guarantees and Commitments [Abstract]
Unused revolving credit line commitments and other	$ 3,435	$ 2,341
Commitments to provide capital to investees	394	283
Commitment to fund remaining unused balances on home equity lines of credit	253	318
Mortgage loan origination commitments	171	95
Construction-lending commitments	$ 85	$ 144