Fair Values of Assets and Liabilities Fair Value of Assets & Liabilities (Non-Recurring) (Details 5) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 165,737	$ 165,883
Nonconsolidated VIEs [Member] | Affordable housing partnerships
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	187	200
Nonconsolidated VIEs [Member] | Affordable housing partnerships | Non-recurring basis [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 97	$ 101