Fair Values of Assets and Liabilities Fair Value of Assets & Liabilities (Non-Recurring) (Details) - Nonconsolidated VIEs [Member] - Affordable housing partnerships and other real estate partnerships[Member] - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Affordable housing partnerships, carrying value	$ 385	$ 408
Non-recurring basis [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Affordable housing partnerships, carrying value	$ 121	$ 166