Investment Securities (Tables)

3 Months Ended

Mar. 31, 2017

Investment Securities (Tables) [Abstract]

Schedule of Available for Sale Securities by Type

The following is a summary of investment securities as of March 31, 2017 and December 31, 2016:

	2017								2016
				Gross		Gross		Estimated				Gross		Gross		Estimated
				Unrealized		Unrealized		Fair				Unrealized		Unrealized		Fair
Description of Securities (Millions)		Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
State and municipal obligations	$	1,686	$	24	$	(4)	$	1,706	$	2,019	$	28	$	(11)	$	2,036
U.S. Government agency obligations		12		―		―		12		12		―		―		12
U.S. Government treasury obligations		1,135		7		(6)		1,136		465		3		(8)		460
Corporate debt securities		19		―		―		19		19		―		―		19
Mortgage-backed securities ^(a)		87		3		―		90		92		3		―		95
Equity securities		1		―		―		1		1		―		―		1
Foreign government bonds and obligations		549		1		(1)		549		486		1		(1)		486
Other ^(b)		50		―		(2)		48		50		―		(2)		48
Total	$	3,539	$	35	$	(13)	$	3,561	$	3,144	$	35	$	(22)	$	3,157

Represents mortgage-backed securities guaranteed by Fannie Mae, Freddie Mac or Ginnie Mae.
Other comprises investments in various mutual funds.

Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value

The following table provides information about the Company’s investment securities with gross unrealized losses and the length of time that individual securities have been in a continuous unrealized loss position as of March 31, 2017 and December 31, 2016:

	2017								2016
	Less than 12 months				12 months or more				Less than 12 months				12 months or more
				Gross				Gross				Gross				Gross
Description of Securities (Millions)		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
State and municipal obligations	$	98	$	(4)	$	―	$	―	$	153	$	(11)	$	―	$	―
U.S. Government treasury obligations		299		(6)		―		―		298		(8)		―		―
Other		―		―		32		(2)		―		―		32		(2)
Total	$	397	$	(10)	$	32	$	(2)	$	451	$	(19)	$	32	$	(2)

Available for Sale Securities Ratio of Fair Value to Amortized Cost

The following table summarizes the gross unrealized losses due to temporary impairments by ratio of fair value to amortized cost as of March 31, 2017 and December 31, 2016:

	Less than 12 months					12 months or more					Total
Ratio of Fair Value to					Gross					Gross					Gross
Amortized Cost	Number of		Estimated		Unrealized	Number of		Estimated		Unrealized	Number of		Estimated		Unrealized
(Dollars in millions)	Securities		Fair Value		Losses	Securities		Fair Value		Losses	Securities		Fair Value		Losses
2017:
90%–100%	21	$	397	$	(10)	6	$	32	$	(2)	27	$	429	$	(12)
Total as of March 31, 2017	21	$	397	$	(10)	6	$	32	$	(2)	27	$	429	$	(12)

2016:
90%–100%	33	$	411	$	(13)	6	$	32	$	(2)	39	$	443	$	(15)
Less than 90%	4		40		(6)	―		―		―	4		40		(6)
Total as of December 31, 2016	37	$	451	$	(19)	6	$	32	$	(2)	43	$	483	$	(21)

Contractual maturities of investment securities

Contractual maturities for investment securities with stated maturities as of March 31, 2017 were as follows:

				Estimated
(Millions)		Cost		Fair Value
Due within 1 year	$	689	$	690
Due after 1 year but within 5 years		990		992
Due after 5 years but within 10 years		365		369
Due after 10 years		1,446		1,462
Total	$	3,490	$	3,513