Fair Value Measurements (Assets Measured on a Nonrecurring Basis, Level 3 Quantitative Information) (Details) - Nonrecurring - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Repossessed assets	$ 15	$ 17
Residential first mortgage loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment	22	40
Commercial and industrial
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment	1	2
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Repossessed assets	15	17
Level 3 | Residential first mortgage loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment	22	40
Level 3 | Residential first mortgage loans | Fair value of underlying collateral
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment	$ 22	$ 40
Level 3 | Residential first mortgage loans | Fair value of underlying collateral | Lower range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	23.00%	35.00%
Level 3 | Residential first mortgage loans | Fair value of underlying collateral | Upper range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	28.00%	45.00%
Level 3 | Residential first mortgage loans | Fair value of underlying collateral | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	25.60%	35.20%
Level 3 | Commercial and industrial
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment	$ 1	$ 2
Level 3 | Commercial and industrial | Fair value of underlying collateral
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment	$ 1
Level 3 | Commercial and industrial | Fair value of underlying collateral | Lower range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	50.00%
Level 3 | Commercial and industrial | Fair value of underlying collateral | Upper range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	55.00%
Level 3 | Commercial and industrial | Fair value of underlying collateral | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	53.40%
Level 3 | Commercial real estate | Fair value of underlying collateral
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans held-for-investment		$ 2
Level 3 | Commercial real estate | Fair value of underlying collateral | Lower range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)		45.00%
Level 3 | Commercial real estate | Fair value of underlying collateral | Upper range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)		55.00%
Level 3 | Commercial real estate | Fair value of underlying collateral | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)		50.10%
Level 3 | Repossessed assets | Fair value of underlying collateral
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Repossessed assets	$ 15
Level 3 | Repossessed assets | Fair value of underlying collateral | Lower range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	35.00%	16.00%
Level 3 | Repossessed assets | Fair value of underlying collateral | Upper range
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	98.00%	100.00%
Level 3 | Repossessed assets | Fair value of underlying collateral | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loss severity (as a percent)	61.70%	48.70%