Employee Benefits - Pension Plan Assets by Asset Category (Details) (Pension Plans, USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Apr. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 618	$ 531	$ 178	$ 174
Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	618		178
Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12		17
Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	348		161
Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	258		0
Cash and cash equivalents | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22		15
Cash and cash equivalents | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4		0
Cash and cash equivalents | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18		15
Cash and cash equivalents | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Equity Funds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	96		82
Equity Funds | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Equity Funds | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	96		82
Equity Funds | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Equity Securities | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20		17
Equity Securities | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20		17
Equity Securities | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Equity Securities | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
U.S. treasuries and agencies | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	180		25
U.S. treasuries and agencies | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
U.S. treasuries and agencies | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	180		25
U.S. treasuries and agencies | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Corporate bonds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16		9
Corporate bonds | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Corporate bonds | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16		9
Corporate bonds | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Other fixed income | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	26		30
Other fixed income | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(12)		0
Other fixed income | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	38		30
Other fixed income | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0		0
Hedge funds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	258
Hedge funds | Level 1 (quoted prices in active markets)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Hedge funds | Level 2 (significant observable input)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Hedge funds | Level 3 (significant unobservable inputs)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 258